Polypropylene/ethylene polymer fiber having improved bond performance and composition for making the same

ABSTRACT

The subject invention is directed to fibers and polymer blend compositions having improved bonding performance. In particular, the subject invention pertains to a multiconstituent fiber comprising a blend of a polypropylene polymer and a high molecular weight (i.e. low melt index or melt flow) ethylene polymer. The subject invention further pertains to the use of the fiber and polymer blend composition which has improved bonding performance in various end-use applications, especially woven and nonwoven fabrics such as, for example, disposable incontinence garments and diapers. The fibers have good spinnability and provide fabrics having improved bond strength and elongation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority and a division to prior U.S. patentapplication Ser. No. 09/456,595 filed on Dec. 8, 1999, and now U.S. Pat.No. 6,281,289 which claims priority to a prior U.S./foreign/Provisionalpatent application Serial No. 60/111,443, filed Dec. 8, 1998 entitled“Polypropylene/Ethylene Polymer Fiber Having Improved Bond Performanceand Composition for Making the Same.”

FIELD OF THE INVENTION

This invention relates to polymer compositions having improved bondingperformance. In particular, the subject invention pertains to a polymercomposition comprising a blend of a polypropylene polymer and a highmolecular weight (i.e low melt index or melt flow) ethylene polymer. Thesubject invention further. pertains to the use of the polymer blendcomposition which has improved bonding performance in various end-useapplications, especially fibers, nonwovenfabrics and other articlesfabricated from fibers (e.g., disposable incontinence garments anddiapers). The fibers have good spinnability and provide a fabric havinggood bond strength and good elongation.

BACKGROUND

Fiber is typically classified according to its diameter. Monofilamentfiber is generally defined as having an individual fiber diametergreater than 15 denier, usually greater than 30 denier per filament.Fine denier fiber generally refers to a fiber having a diameter lessthan 15 denier per filament. Microdenier fiber is generally defined asfiber having less than 100 microns diameter. The fiber can also beclassified by the process by which it is made, such as monofilament,continuous wound fine filament, staple or short cut fiber, spun bond,and melt blown fiber.

A variety of fibers and fabrics have been made from thermoplastics, suchas polypropylene, highly branched low density polyethylene (LDPE) madetypically in a high pressure polymerization process, linearheterogeneously branched polyethylene (e.g., linear low densitypolyethylene made using Ziegler catalysis), blends of polypropylene andlinear heterogeneously branched polyethylene, blends of linearheterogeneously branched polyethylene, and ethylene/vinyl alcoholcopolymers.

Of the various polymers known to be extrudable into fiber, highlybranched LDPE has not been successfully melt spun into fine denierfiber. Linear heterogeneously branched polyethylene has been made intomonofilament, as described in U.S. Pat. No. 4,076,698 (Anderson et al.),the disclosure of which is incorporated herein by reference. Linearheterogeneously branched polyethylene has also been successfully madeinto fine denier fiber, as disclosed in U.S. Pat. No. 4,644,045(Fowells), U.S. Pat. No. 4,830,907 (Sawyer et al.), U.S. Pat. No.4,909,975 (Sawyer et al.) and in U.S. Pat. No. 4,578,414 (Sawyer etal.), the disclosures of which are incorporated herein by reference.Blends of such heterogeneously branched polyethylene have also beensuccessfully made into fine denier fiber and fabrics, as disclosed inU.S. Pat. No. 4,842,922 (Krupp et al.), U.S. Pat. No. 4,990,204 (Kruppet al.) and U.S. Pat. No. 5,112,686 (Krupp et al.), the disclosures ofwhich are all incorporated herein by reference. U.S. Pat. No. 5,068,141(Kubo et al.) also discloses making nonwoven fabrics from continuousheat bonded filaments of certain heterogeneously branched LLDPE havingspecified heats of fusion. While the use of blends of heterogeneouslybranched polymers produces improved fabric, the polymers are moredifficult to spin without fiber breaks and/or dripping at the spinneretdie.

U.S. Pat. Nos. 5,294,492 and 5,593,768 (Gessner), both incorporatedherein by reference, describe a multiconstituent fiber having improvedthermal bonding characteristics composed of a blend of at least twodifferent thermoplastic polymers which form a continuous polymer phaseand at least one noncontinuous polymer phase. In the Claims, Gessnerrecites that the at least one noncontinuous phase occupies a substantialportion of the surface of the fiber made from the blend. But while webelieve the claims in U.S. Pat. Nos. 5,294,492 and 5,593,768 specify,for example, a core-sheath configuration with respect to the polymerphases, the photomicrograph (FIG. 1 therein) shows an island-sea typephase configuration for the fiber cross-section. Further, we believe itis the continuous polymer phase (not the noncontinuous phase) whichoccupies a substantial portion of the surface of the fiber exemplified(but not claimed) by Gessner. Also, all of the Examples (and presumablyFIG. 1 therein) consist of polypropylene polymer blended with ASPUN™fiber grade LLDPE resins having a 12 or 26 g/10 minute I₂ melt index assupplied by The Dow Chemical Company. The exemplar polypropylene polymerused by Gessner was described a “controlled rheology” PP (i.e. avisbroken PP) having a melt flow rate of 26 and at least 90 percent byweight isotacticity.

U.S. Pat. No. 5,549,867 (Gessner et al.), incorporated herein byreference, describes the addition of a low molecular weight (i.e. highmelt index or melt flow) polyolefin to a polyolefin with a molecularweight (M_(z)) of from 400,000 to 580,000 to improve spinning. TheExamples set forth in Gessner et al. are all directed to blends of 10 to30 weight percent of a lower molecular weight metallocene polypropylenewith from 70 to 90 weight percent of a higher molecular weightpolypropylene produced using a Ziegler-Natta catalyst.

U.S. Pat. No. 4,839,228 (Jezic et al.), incorporated herein byreference, describes biconstituent fibers having improved tenacity andhand composed of a highly crystalline polypropylene polymer with LDPE,HDPE or preferably LLDPE. The polyethylene resins are described to havea moderately high molecular weight wherein their I₂ melt index is in therange of from about 12 to about 120 g/10 minutes.

Also, fibers made from blends of visbroken polypropylene polymer andhomopolymer high density polyethylene (HDPE) having an I₂ melt index ofequal to greater than 5 g/10 minutes are known. Such blends are thoughtto function on the basis of the immiscibility of the olefin polymers.

WO 95/32091 (Stahl et al.) discloses a reduction in bonding temperaturesby utilizing blends of fibers produced from polypropylene resins havingdifferent melting points and produced by different fiber manufacturingprocesses, e.g., meltblown and spunbond fibers. Stahl et al. claims afiber comprising a blend of an isotactic propylene copolymer with ahigher melting thermoplastic polymer.

WO 96/23838, U.S. Pat. Nos. 5,539,056 and 5,516,848, the disclosures ofwhich are incorporated herein by reference, teach blends of an amorphouspoly-α-olefin of Mw>150,000 (produced via single site catalysis) and acrystalline poly-α-olefin with Mw<300,000, (produced via single sitecatalysis) in which the molecular weight of the amorphous polypropyleneis greater than the molecular weight of the crystalline polypropylene.Preferred blends are described to comprise about 10 to about 90 weightpercent of amorphous polypropylene. The described blends are said toexhibit unusual elastomeric properties, namely an improved balance ofmechanical strength and rubber recovery properties.

U.S. Pat. No. 5,483,002 and EP 643100, the disclosures of both of whichare incorporated herein by reference, teach blends of a semi-crystallinepropylene homopolymer having a melting point of 125 to 165° C. and asemi-crystalline propylene homopolymer having a melting point below 130°C. or a non-crystallizing propylene homopolymer having a glasstransition temperature which is less than or equal to −10° C. Theseblends are said to have improved mechanical properties, notably impactstrength.

Crystalline polypropylenes produced by single site catalysis have beenreported to be particularly suited for fiber production. Due to narrowmolecular weight distributions and low amorphous contents, higherspinning rates and higher tenacities have been reported. But, isotacticPP fibers, in general (and particularly when produced using single sitecatalyst) exhibit poor bonding performance.

U.S. Pat. No. 5,677,383 (Lai et al.), incorporated herein by reference,discloses blends of (A) at least one homogeneously branched ethylenepolymer having a high slope of strain hardening coefficient and (B) atleast one ethylene polymer having a high polymer density and some amountof a linear high density polymer fraction. The Examples set forth by Laiet al. are directed to substantially linear ethylene interpolymersblended with heterogeneously branched ethylene polymers. Lai et al.describe the use of their blends in a variety of end use applications,including fibers. The disclosed compositions preferably comprise asubstantially linear ethylene polymer having a density of at least 0.89grams/centimeters³. But Lai et al. disclosed fabrication temperaturesonly above 165° C. In contrast, to preserve fiber integrity, fabrics arefrequently bonded at temperatures less than 165° C. such that all of thecrystalline material is not melted before or during the fiber bondingstep.

While various olefin polymer compositions have found success in a numberof fiber and fabric applications, the fibers made from such compositionswould benefit from an improvement in bond strength, which would lead tostronger fabrics, and accordingly to increased value to the nonwovenfabric and article manufacturers, as well as to the ultimate consumer.But any benefit in bond strength must not be at the cost of adetrimental reduction in spinnability and fiber elongation nor adetrimental increase in the sticking of the fibers or fabric toequipment during processing.

SUMMARY OF THE INVENTION

We have discovered that the inclusion of a high molecular weightethylene polymer into a polypropylene. polymer provides amulticonstituent fiber and calendered fabric having an improved bondperformance, while simultaneously maintaining excellent fiber spinningand elongation performance. Accordingly, the subject invention providesa fiber having a diameter in a range of from 0.1 to 50 denier andcomprising:

(A) from about 0.5 percent to about 25 weight percent (by weight of thefiber) of at least one ethylene polymer having:

i. an I₂ melt index less than or equal to 10 grams/10 minutes,preferably less than 5 g/ 10 minutes, more preferably less than or equalto 3 g/10 minutes, most preferably less than or equal to 1.5 g/10minutes, especially less than or equal to 0.75 g/10 minutes and

ii. a density of from about 0.85 to about 0.97 grams/centimeters³, asmeasured in accordance with ASTM D792, (or a corresponding percentcrystallinity in range of about 12 to about 81 percent by weight, asdetermined using differential scanning calorimetry (DSC)), and

(B) a polypropylene polymer, preferably a polypropylene polymer having amelt flow rate (MFR) in the range of about 1 to about 1000 grams/10minutes, measured in accordance with ASTM DI 238 at 230° C./2.16 kg,more preferably in range of about 5 to about 100 grams/10 minutes,

with the proviso that where the ethylene polymer is an ethylene/α-olefininterpolymer having an I₂ melt index in the range of about 5 to about 10g/10 minutes, the density of the ethylene/α-olefin polymer is greaterthan 0.87 g/cm³, preferably greater than or equal to 0.90 g/cm³, andmore preferably greater than or equal to 0.94 g/cm³, as measured inaccordance with ASTM D792,

with the proviso that where the ethylene polymer is an ethylenehomopolymer or ethylene/α-olefin interpolymer having a density greaterthan or equal to 0.94 g/cm³, as measured in accordance with ASTM D792,the I₂ melt index of the ethylene polymer is less than 5 g/10 minutes,preferably less than or equal to 3 g/10 minutes, more preferably lessthan or equal to 1.5 g/10 minutes, most preferably less than or equal to0.75 g/10 minutes, and wherein the fiber is thermal bondable at 340pounds/linear inch and a bond roll surface temperature in the range of127 to 137° C.

In a particular aspect, the subject invention provides a fiber having adiameter in a range of from 0.1 to 50 denier, a continuous polymer phaseand at least one discontinuous polymer phase which comprises:

(A) as the at least one discontinuous polymer phase, from about 0.1percent to about 30 weight percent (by weight of the fiber) of at leastone ethylene polymer having:

i. an I₂ melt index less than or equal to 10 grams/10 minutes, and

ii. a density of from about 0.85 to about 0.97 grams/centimeters³, and

(B) as the continuous polymer phase, a polypropylene polymer,

with the proviso that where the ethylene polymer is an ethylene/α-olefininterpolymer having an I₂ melt index in the range of about 5 to about 10g/10 minutes, the density of the ethylene/α-olefin polymer is greaterthan 0.87 g/cm³ (or has a DSC percent crystallinity greater than 13weight percent), preferably greater than or equal to 0.90 g/cm³ (or hasa DSC percent crystallinity greater than 33 weight percent) and morepreferably greater than or equal to 0.94 g/cm³ (or has a DSC percentcrystallinity greater than 60 weight percent),

with the proviso that where the ethylene polymer is an ethylenehomopolymer or ethylene/α-olefin interpolymer having a density greaterthan or equal to 0.94 g/cm³, the I₂ melt index of the ethylene polymeris less than 5 g/10 minutes,

wherein, prior to any bonding operation, the continuous polymer phaseconstitutes more than 50 percent of the fiber surface area and the twopolymer phases cross-sectionally provide an island-sea configuration,and wherein the fiber is thermal bondable at 340 pounds/linear inch anda bond roll surface temperature in the range of 127 to 137° C.

In specific embodiments, the discontinuous phase constitutes an amountof the fiber surface area which is within or less than 50 percent,preferably 25 percent, more preferably 10 percent of amount contained inthe blend composition. That is, in such embodiments, the surface areapercentage of the discontinuous phase polymer is insubstantial as itclosely approximates the total composition weight percentage of thediscontinuous phase polymer), as determined using an electron microscopytechnique which may include selective staining to enhance resolution.

Preferably, the fiber of the invention will be prepared from a polymerblend composition comprising:

(A) at least one homogeneously branched ethylene polymer, morepreferably at least one substantially linear ethylene/α-olefininterpolymer having:

i. a melt flow ratio, I₁₀/I₂,≧5.63,

ii. a molecular weight distribution, M_(w)/M_(n), defined by theequation:

M_(w)M_(n), ≦(I₁₀/I₂)−4.63,

and

iii. a critical shear rate at onset of surface melt fracture of at least50 percent greater than the critical shear rate at the onset of surfacemelt fracture of a linear ethylene polymer having about the same I₂ andM_(W)/M_(n), and

which constitutes the discontinuous polymer phase, and

(B) at least one isotactic polypropylene propylene.

The subject invention further provides a method for improving thebonding strength of a fine denier fiber comprised of at least onepolypropylene polymer, the method comprising providing in an intimateadmixture therewith less than or equal to 22 weight percent, preferablyless than or equal to 17 weight percent, more preferably less than orequal to 12 weight percent of at least one ethylene polymer having adensity of from about 0.85 to about 0.97 g/cm³ and an I₂ melt index offrom about 0.01 to about 10 grams/10 minutes, with the proviso thatwhere the ethylene polymer is an ethylene/α-olefin interpolymer havingan I₂ melt index in the range of about 5 to about 10 g/10 minutes, thedensity of the ethylene/α-olefin polymer is greater than 0.87 g/cm³ andwith the proviso that where the ethylene polymer is an ethylenehomopolymer or ethylene/α-olefin interpolymer having a density greaterthan or equal to 0.94 g/cm³, the I₂ melt index of the ethylene polymeris less than 5 g/10 minutes.

The subject invention further provides a polymer composition havingimproved bond strength comprising:

(A) from about 0.1 percent to about 30 weight percent (by weight of thecomposition) of at least one ethylene polymer having:

i. an I₂ melt index less than or equal to 10 grams/10 minutes, and

iii. a density of from about 0.85 to 0.97 grams/centimeters³, and

(B) a polypropylene polymer,

with the proviso that where the ethylene polymer is an ethylene/α-olefininterpolymer having an I₂ melt index in the range of about 5 to about1.0 g/10 minutes, the density of the ethylene/α-olefin polymer isgreater than 0.87 g/cm³ and with the proviso that where the ethylenepolymer is an ethylene homopolymer or ethylene/α-olefin interpolymerhaving a density greater than or equal to 0.94 g/cm³, the I₂ melt indexof the ethylene polymer is less than 5 g/10 minutes.

The subject invention further provides a polymer composition of theinvention, in the form of a fiber, fabric, nonwoven or woven article,rotomolded article, film layer, injection molded article, thermoformedarticle, blow molded article, injection blow molded article, orextrusion coating composition.

The inventive fibers and fabrics can be produced on conventionalsynthetic fiber or fabric processes (e.g., carded staple, spun bond,melt blown, and flash spun) and they can be used to produce fabricshaving high elongation and tensile strength, without a significantsacrifice in fiber spinnability. As an unexpected surprise, the polymerblend exhibits excellent fiber spinnability even though the ethylenepolymer is characterized as having a high molecular weight. In fact,excellent polymer blend spinnability is achieved even where the ethylenepolymer itself is not spinnable into fine denier fibers (that is,diameters less than about 50 denier) when used alone.

It is also surprising that improved bond strength is obtained withoutcommensurate reductions in elongation performance.

It is a further surprise that relative to known PP/HDPE blends, improvedbond strengths are obtained at relatively low polymer densities andcrystallinities.

It is still another surprise that inventive blends based on highmolecular weight ethylene/aromatic vinyl interpolymers providedramatically improved bond strengths relative to comparative blendsbased on ethylene/α-olefin interpolymers having comparablecrystallinities and melt indexes.

As another surprise, the invention where the polypropylene polymer (B)is manufactured using a metallocene or single-site or constrainedgeometry catalyst system results in substantially stable bond strengthsat about 340 pli in the bonding temperature range of from about 127 toabout 137° C.

These and other embodiments are more fully described in the detaileddescription in conjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a transmission electron microscopy photomicrograph of thecross-section of an inventive fiber (Inventive Example 1) showing acontinuous polypropylene polymer phase and discontinuous ethylenepolymer (stained dark) phase.

FIG. 2 is a transmission electron microscopy photomicrograph of thecross-section of an inventive fiber (Inventive Example 3) showing acontinuous polypropylene polymer phase and discontinuous ethylenepolymer (stained dark) phase.

FIG. 3 is a transmission electron microscopy photomicrograph of thecross-section of an inventive fiber (Inventive Example 9) showing acontinuous polypropylene polymer phase and discontinuous ethylenepolymer (particles with stained dark peripheries) phase.

FIG. 4 is a transmission electron microscopy photomicrograph of thecross-section of a comparative fiber (comparative example 7) showing acontinuous polypropylene polymer phase and discontinuous ethylenepolymer (stained dark dispersed particles) phase.

FIG. 5 is a transmission electron microscopy (TEM) photomicrograph ofthe cross-section of a comparative fiber (comparative example 12)showing a continuous polypropylene polymer phase and discontinuousethylene polymer (highly dispersed stained dark particles) phase.

FIG. 6 is a bar chart illustrating the fabric thermal bond strength ofInventive Examples 1-3 and comparative example 4.

FIG. 7 is a bar chart illustrating the fabric thermal bond strength ofInventive Examples 1, 5 and 6 and comparative example 4.

FIG. 8 is a bar chart illustrating the fabric thermal bond strength ofInventive Examples 1, 8, and 9 and comparative examples 4, 7, 10, 11 and12.

FIG. 9 is a bar chart illustrating the fabric thermal bond strength ofInventive Examples 1 and 2 and comparative examples 4,13, and 14.

FIG. 10 is a bar chart illustrating the fabric thermal bond strength ofInventive Examples 1 and 6 and comparative examples 4 and 15.

FIG. 11 is a bar chart illustrating the fabric thermal bond elongationof Inventive Examples 1-3 and comparative example 4.

FIG. 12 is a bar chart illustrating the fabric thermal bond elongationof Inventive Examples 1, 5 and 6 and comparative example 4.

FIG. 13 is a bar chart illustrating the fabric thermal bond elongationof Inventive Examples 1, 8, and 9 and comparative examples 4, 7, 10, 11and 12.

FIG. 14 is a bar chart illustrating the fabric thermal bond elongationof Inventive Examples 1 and 2 and comparative examples 4,13, and 14.

FIG. 15 is a bar chart illustrating the fabric thermal bond elongationof Inventive Examples 1 and 6 and comparative examples 4 and 15.

FIG. 16 is a bar chart illustrating the fabric thermal bond strength ofInventive Examples 16 and 17 and comparative examples 18 and 19.

FIG. 17a-d are lighted microscope photomicrographs of thermally bondedinventive fibers (Inventive Example 1) and comparative fibers(comparative example 4) at 25× and 200× magnification.

FIG. 18a-d are lighted microscope photomicrographs of thermally bondedinventive fibers (Inventive Example 1) and comparative fibers(comparative example 4) at 50 μm and 20 μm magnification.

FIG. 19 is a transmission electron microscopy (TEM) photomicrograph at15,000× magnification of the bond cross-section of thermally bondedinventive fibers (Inventive Example 1) showing a continuouspolypropylene polymer phase and a discontinuous ethylene polymer(stained dark) phase.

FIG. 20 is a transmission electron microscopy (TEM) photomicrograph at15,000× magnification of the bond cross-section of several thermallybonded comparative fibers (comparative example 4) showing stress crazing(stained dark) within the continuous polypropylene polymer matrix.

DETAILED DESCRIPTION OF THE INVENTION

The term “bonding” as used herein refers to the application of force orpressure (separate from or in addition to that required or used to drawfibers to less than or equal to 50 denier) to fuse molten or softenedfibers together such that a bond strength of greater than or equal to1,500 grams results. The term “thermal bonding” is used herein refers tothe reheating of staple fibers and the application of force or pressure(separate from or in addition to that required or used to draw fibers toless than or equal to 50 denier) to effect the a melting (or softening)and fusing of fibers such that a bond strength of greater than or equalto 2,000 grams results. Operations that drawing and fuse fibers togetherin a single or simultaneous operation, or prior to any take-up roll (forexample, a godet) such as, for example, spunbonding are not consider tobe a thermal bonding operation, although the inventive fiber can havethe form of or result from a spunbonding operation and similar fibermaking operations.

The terms “visbroken” and “viscracked” are used herein in theirconventional sense to refer to a reactor grade or product polypropylenepolymer which is subsequently cracked or chain-scissioned prior to,during or by extrusion to provide a substantially higher melt flow rate.In the present invention, a viscracked polypropylene polymer will show aMFR change of 3:1, especially, 5:1 and more especially 7:1 in respect tothe ratio of its subsequent MFR to initial MFR. For example, but theinvention is not limited thereto, a reactor grade polypropylene polymerhaving a MFR of 4 can be used in the present invention where it isvisbroken or viscracked to a MFR greater than about 20 (i.e., havinga >20 visbroken MFR) prior to, during or by extrusion (for example, inan extruder immediately prior to a spinneret) in a conventional fibermaking operation. In the present invention, to facilitate visbreaking,an initiator such as a peroxide (for example, but not limited to,Lupersol™ 101) and optionally antioxidant can be compounded with theinitially low MFR polypropylene polymer prior to fiber making. In oneembodiment, the polypropylene polymer is provided in powder form and theperoxide, antioxidant and ethylene polymer are admixed via a side-armextrusion at the polypropylene polymer manufacturing facility.Polypropylene polymers having a visbroken melt flow rate are alsoreferred to in the art as “controlled rheology polypropylene” (see,e.g., Gessner in U.S. Pat. No. 5,593,768) and initiator-assisteddegraded polypropylene (see, e.g. Polypropylene Handbook, HanserPublishers, New York (1996), the disclosure of which is incorporated byreference).

The term “reactor grade” is used herein in its conventional sense torefer to a virgin or additive modified polypropylene polymer which isnot cracked or chain-scissioned after its initial production and as suchits MFR will not be substantially changed during or by extrusion (forexample, in an extruder immediately prior to a spinneret). In thepresent invention, reactor grade polypropylene will have MFR changeduring extrusion of less than 3:1, especially less than or equal to 2:1,more especially less than or equal to 1.5:1, most especially less thanor equal to 1.25:1 with respect to the ratio of the polymer's subsequentMFR to its initial (before extrusion) MFR. In the present invention,reactor grade polypropylene polymers characterized as having asubsequent to initial MFR ratio of less than or equal to 1.25:1typically contain an effective thermal stabilizer system such as, forexample, but not limited to, 1 total weight percent Irganox™ 1010phenolic antioxidant or Irgafos™ 168 phosphite stabilizer or both.Reactor grade polypropylene polymers characterized as having a relativelow subsequent to initial MFR ratio are referred to in the art as“constant rheology polypropylene” (see Jezic et al. U.S. Pat. No.4,839,228).

The term “excellent spinnability” is used herein to refer to the abilityto produce high quality fine denier fibers using at leastsemi-commercial equipment (if not commercial equipment) at at leastsemi-commercial production rates (if not commercial production rates).Representative of excellent spinnability is producing fine denier fiberat greater than or equal to 750 meters/minute without any drips usingthe spinnability test described by Pinoca et al. in U.S. Pat. No.5,631,083, the disclosure of which is incorporated herein by reference.

The term “stable bond strength” is used herein to mean that the thermalbond strength for the fabricated article (e.g. fiber) is in the range of4,000 to 6,000 grams as determined at about 340 pli and bondingtemperatures in the range of 127-137° C.

The term “fine denier fiber” is used herein to refer to fibers having adiameter less than or equal to 50 denier.

The polymer blend composition used to make the fiber and fabric of thepresent invention comprises at least one polypropylene polymerpreferably a crystalline polypropylene polymer. The polypropylenepolymer can be coupled, branched, visbroken or a reactor grade resin.The inventive composition comprises from about 70 to about 99.9 weightpercent of at least one polypropylene polymer. In certain embodiments,inventive composition comprises equal to or greater than 78 weightpercent, especially equal to or greater than 83 weight percent and moreespecially equal to or greater than 88 weight percent of at least onepolypropylene polymer.

A crystalline polypropylene polymer is a polymer with at least about 90mole percent of its repeating units derived from propylene, preferablyat least about 97 percent, more preferably at least about 99 percent.The term “crystalline” is used herein to mean isotactic polypropylenehaving at least about 93 percent isotactic triads as measured by ¹³CNMR, preferably at least about 95 percent, more preferably at leastabout 96 percent.

The polypropylene polymer comprises either homopolymer polypropylene orpropylene polymerized with one or more other monomers additionpolymerizable with propylene. The other monomers are preferably olefins,more preferably alpha olefins, most preferably ethylene or an olefinhaving a structure RCH═CH₂ where R is aliphatic or aromatic and has atleast two and preferably less than about 18 carbon atoms. Hydrocarbonolefin monomers within the skill in the art, include hydrocarbons havingone or more double bonds at least one of which is polymerizable with thealpha olefin monomer.

Suitable alpha olefins for polymerizing with propylene include 1-butene,1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-unidecene,1-dodecene and the like as well as 4-methyl-1-pentene,4-methyl-1-hexene, 5-methyl-1-hexene, vinylcyclohexane, styrene and thelike. The preferred alpha olefins include ethylene, 1-butene, 1-hexene,and 1-octene.

Optionally, but not in the most preferred embodiment of the presentinvention, the polypropylene polymer comprises monomers having at leasttwo double bonds which are preferably dienes or trienes. Suitable dieneand triene comonomers include 7-methyl-1,6-octadiene,3,7-dimethyl-1,6-octadiene, 5,7-dimethyl-1,6-octadiene,3,7,11-trimethyl-1,6,10-octatriene, 6-methyl-1,5-heptadiene,1,3-butadiene, 1,6-heptadiene, 1,7-octadiene, 1,8-nonadiene,1,9-decadiene, 1,10-undecadiene, norbornene, tetracyclododecene, ormixtures thereof, preferably butadiene, hexadienes, and octadienes, mostpreferably 1,4-hexadiene, 1,9-decadiene, 4-methyl-1,4-hexadiene,5-methyl-1,4-hexadiene, dicyclopentactiene, and5-ethylidene-2-norbornene.

Suitable polypropylenes are formed by means within the skill in the art,for example, using single site catalysts or Ziegler Natta catalysts. Thepropylene and optional alpha-olefin monomers are polymerized underconditions within the skill in the art, for instance as disclosed byGalli, et al., Angew. Macromol. Chem., Vol. 120, 73 (1984), or by E. P.Moore, et al. in Polypropylene Handbook, Hanser Publishers, New York,1996, particularly pages 11-98, the disclosures of which areincorporated herein by reference.

The polypropylene polymer used in the present invention is suitably ofany molecular weight distribution (MWD). Polypropylene polymers of broador narrow MWD are formed by means within the skill in the art. For fiberapplications, generally a narrower MWD is preferred (for example, aM_(w)/M_(n) ratio or polydispersity of less than or equal to 3).Polypropylene polymers having a narrow MWD can be advantageouslyprovided by visbreaking or by manufacturing reactor grades(non-visbroken) using single-site catalysis or both.

Polypropylene polymers for use in the present invention preferably havea weight average molecular weight as measured by gel permeationchromatography (GPC) greater than about 100,000, preferably greater thanabout 115,000, more preferably greater than about 150,000, mostpreferably greater than about 250,000 to obtain desirably highmechanical strength in the final product.

Preferably, the polypropylene polymer has a melt flow rate (MFR) in therange of about 1 to about 1000 grams/10 minutes, more preferably inrange of about 5 to about 100 grams/10 minutes, as measured inaccordance with ASTM D1238 at 230° C./2.16 kg.

In general, for fiber making, especially fiber spinning, the melt flowrate of the polypropylene polymer is preferably greater than or equal to20 g/10 minutes, more preferably greater than or equal to 25 g/10minutes, and especially in the range of from about 25 to about 50 g/10minutes, most especially from about 30 to about 40 g/10 minutes.

But specifically for staple fiber, the melt flow rate (MFR) of thepolypropylene polymer is preferably in the range of about 10 to about 20g/10 minutes. For. spunbond fiber, the melt flow rate (MFR) of thepolypropylene polymer is preferably in the range of about 20 to about 40g/10 minutes. For melt blown fiber, the melt flow rate (MFR) of thepolypropylene polymer is preferably in the range of about 500 to about1500 g/10 minutes. For gel spun fiber, the melt flow rate (MFR) of thepolypropylene polymer is preferably less than or equal to 1 g/10minutes.

The polypropylene polymer used in the present invention can be branchedor coupled to provide increased nucleation and crystallization rates.The term “coupled” is used herein to refer to polypropylene polymerswhich are rheology-modified such that they exhibit a change in theresistance of the molten polymer to flow during fiber making operation(for example, in the extruder immediately prior to the spinneret in afiber spinning operation. Whereas “visbroken” is in the direction ofchain-scission, “coupled” is in the direction of crosslinking ornetworking. An example of coupling is where a couple agent (for example,an azide compound) is added to a relatively high melt flow ratepolypropylene polymer such that after extrusion the resultantpolypropylene polymer composition attains a substantially lower meltflow rate than the initial melt flow rate. For the coupled or branchedpolypropylene used in the present invention the ratio of subsequent MFRto initial MFR is preferably less than or equal to 0.7:1, morepreferably less than or equal to 0.2:1.

Suitable branched polypropylene for use in the present invention iscommercially available for instance from Montell North America under thetrade designations Profax PF-611 and PF-814. Alternatively, suitablebranched or coupled polypropylene can be prepared by means within theskill in the art such as by peroxide or electron-beam treatment, forinstance as disclosed by DeNicola et al. in U.S. Pat. No. 5,414,027 (theuse of high energy (ionizing) radiation in a reduced oxygen atmosphere);EP 0 190 889 to Himont (electron beam irradiation of isotacticpolypropylene at lower temperatures); U.S. Pat. No. 5,464,907 (AkzoNobel NV); EP 0 754 711 Solvay (peroxide treatment); and U.S. patentapplication Ser. No. 09/133,576, filed August 13,1998 (azide couplingagents); the disclosures of all of which are incorporated herein byreference.

All references herein to elements or metals belonging to a certain Grouprefer to the Periodic Table of the Elements published and copyrighted byCRC. Press, Inc., 1989. Also any reference to the Group or Groups shallbe to the Group or Groups as reflected in this Periodic Table of theElements using the IUPAC system for numbering groups.

Preparation of crystalline polypropylene polymers is well within theskill in the art. Advantageous catalysts for use in preparing narrowmolecular weight distribution polypropylene polymers useful in thepractice of the invention are preferably derivatives of any transitionmetal including Lanthanides, but preferably of Group 3, 4, or Lanthanidemetals which are in the +2, +3, or +4 formal oxidation state. Preferredcompounds include metal complexes containing from 1 to 3 π-bondedanionic or neutral ligand groups, which are optionally cyclic ornon-cyclic delocalized π-bonded anionic ligand groups. Exemplary of suchπ-bonded anionic ligand groups are conjugated or nonconjugated, cyclicor non-cyclic dienyl groups, and allyl groups. By the term “π-bonded” ismeant that the ligand group is bonded to the transition metal by meansof its delocalized π-electrons.

Each atom in the delocalized π-bonded group is optionally independentlysubstituted with a radical selected from the group consisting ofhydrogen, halogen, hydrocarbyl, halohydrocarbyl, hydrocarbyl-substitutedmetalloid radicals wherein the metalloid is selected from Group 14 ofthe Periodic Table of the Elements, and such hydrocarbyl- orhydrocarbyl-substituted metalloid radicals further substituted with aGroup 15 or 16 hetero atom containing moiety. Included within the term“hydrocarbyl” are C₁-C₂₀ straight, branched and cyclic alkyl radicals,C₆-C₂₀ aromatic radicals, C₇-C₂₀ alkyl-substituted aromatic radicals,and C₇-C₂₀ aryl-substituted alkyl radicals. In addition two or more suchadjacent radicals may together form a fused ring system, a hydrogenatedfused ring system, or a metallocycle with the metal.

Suitable hydrocarbyl-substituted organometalloid radicals include mono-,di- and tri-substituted organometalloid radicals of Group 14 elementswherein each of the hydrocarbyl groups contains from 1 to 20 carbonatoms. Examples of advantageous hydrocarbyl-substituted organometalloidradicals include trimethylsilyl, triethylsilyl, ethyidimethylsilyl,methyidiethylsilyl, triphenylgermyl, and trimethylgermyl groups.Examples of Group 15 or 16 hetero atom containing moieties includeamine, phosphine, ether or thioether moieties or monovalent derivativesthereof, e. g. amide, phosphide, ether or thioether groups bonded to thetransition metal or Lanthanide metal, and bonded to the hydrocarbylgroup or to the hydrocarbyl- substituted metalloid containing group.

Examples of advantageous anionic, delocalized π-bonded groups includecyclopentadienyl, indenyl, fluorenyl, tetrahydroindenyl,tetrahydrofluorenyl, octahydrofluorenyl, pentadienyl, cyclohexadienyl,dihydroanthracenyl, hexahydroanthracenyl, and decahydroanthracenylgroups, as well as C₁-C₁₀ hydrocarbyl-substituted or C₁-C₁₀hydrocarbyl-substituted silyl substituted derivatives thereof. Preferredanionic delocalized π-bonded groups are cyclopentaclienyl,pentamethylcyclopentadienyl, tetramethylcyclopentadienvi,tetramethylsilylcyclopentadienyl, indenyl, 2,3dimethylindenyl,fluorenyl, 2-methylindenyl, 2-methyl4-phenytindenyl,tetrahydrofluorenyl, octahydrofluorenyl, and tetrahydroindenyl.

A preferred class of catalysts are transition metal complexescorresponding to the Formula A:

L_(l)MX_(m)X′_(n)X″_(p),

or a dimer thereof wherein:

L is an anionic, delocalized, π-bonded group that is bound to M_(n)containing up to 50 non-hydrogen atoms, optionally two L groups may bejoined together forming a bridged structure, and further optionally oneL is bound to X;

M is a metal of Group 4 of the Periodic Table of the Elements in the +2,+3 or +4 formal oxidation state;

X is an optional, divalent substituent of up to 50 non-hydrogen atomsthat together with L forms a metallocycle with M;

X′ at each occurrence is an optional neutral Lewis base having up to 20non-hydrogen atoms and optionally one X′ and one L may be joinedtogether;

X″ each occurrence is a monovalent, anionic moiety having up to 40non-hydrogen atoms, optionally, two X″ groups are covalently boundtogether forming a divalent dianionic moiety having both valences boundto M, or, optionally two X″ groups are covalently bound together to forma neutral, conjugated or nonconjugated diene that is π-bonded to M(whereupon M is in the +2 oxidation state), or further optionally one ormore X″ and one or more X′ groups are bonded together thereby forming amoiety that is both covalently bound to M and coordinated thereto bymeans of Lewis base functionality;

l is 0, 1 or 2;

m is 0 or 1;

n is a number from 0 to 3;

p is an integer from 0 to 3. and

the sum, l+m+p, is equal to the formal oxidation state of M, except whentwo X″ groups together form a neutral conjugated or non-conjugated dienethat is π-bonded to M, in which case the sum l+m is equal to the formaloxidation state of M.

Preferred complexes include those containing either one or two L groups.The latter complexes include those containing a bridging group linkingthe two L groups. Preferred bridging groups are those corresponding tothe formula (ER*₂)_(x) wherein E is silicon, germanium, tin, or carbon,R* independently each occurrence is hydrogen or a group selected fromsilyl, hydrocarbyl, hydrocarbyloxy and combinations thereof, said R*having up to 30 carbon or silicon atoms, and x is 1 to 8. Preferably, R*independently each occurrence is methyl, ethyl, propyl, benzyl,tert-butyl, phenyl, methoxy, ethoxy or phenoxy.

Examples of the complexes containing two L groups are compoundscorresponding to the formula:

wherein:

M is titanium, zirconium or hafnium, preferably zirconium or hafnium; inthe +2 or +4 formal oxidation state;

R³ in each occurrence independently is selected from the groupconsisting of hydrogen, hydrocarbyl, silyl, germyl, cyano, halo andcombinations thereof, said R³ having up to 20 non-hydrogen atoms, oradjacent R³ groups together form a divalent derivative (e.g., ahydrocarbadiyl, germadiyl group) thereby forming a fused ring system,and V independently each occurrence is an anionic ligand group of up to40 non-hydrogen atoms, or two X″ groups together form a divalent anionicligand group of up to 40 non-hydrogen atoms or together are a conjugateddiene having from 4 to 30 non-hydrogen atoms forming α-complex with M,whereupon M is in the +2 formal oxidation state, and R*, E and x are aspreviously defined.

The foregoing metal complexes are especially suited for the preparationof polymers having stereoregular molecular structure. In such capacityit is preferred that the complex possesses C_(S) symmetry or possesses achiral, stereorigid structure. Examples of the first type are compoundspossessing different delocalized π-bonded systems, such as onecyclopentadienyl group and one fluorenyl group. Similar systems based onTI(IV) or Zr(IV) were disclosed for preparation of syndiotactic olefinpolymers in Ewen, et al., J. Am. Chem. Soc., 110, pp. 6255-6256 (1980),incorporated herein by reference. Examples of chiral structures includerac bis-indenyl complexes. Similar systems based on Ti(IV) or Zr(IV)were disclosed for preparation of isotactic olefin polymers in Wild etal., J. Organomet. Chem., 232, pp. 233-47, (1982), incorporated hereinby reference.

Suitable bridged ligands containing two π-bonded groups are:(dimethylsilyl-bis(cyclopentadienyl)),(dimethylsilyl-bis(methylcyclopentadienyl)),(dimethylsilyl-bis(ethylcyclopentadienyl)),(dimethylsilyl-bis(t-butylcyclopentadienyl)),(dimethylsilyl-bis(tetramethylcyclopentadienyl)),(dimethylsilyl-bis(indenyl)), (dimethylsilyl-bis(tetrahydroindenyl)),(dimethylsilyl-bis(fluorenyl)),(dimethylsilyl-bis(tetrahydrofluorenyl)),(dimethylsilyl-bis(2-methyl-4-phenylindenyl)),(dimethylsilyl-bis(2-methylindenyl)),(dimethylsilyl-cyclopentadienyl-fluorenyl),(dimethylsilyl-cyclopentadienyl-octahydrofluorenyl),(dimethylsilyl-cyclopentadienyl-tetrahydrofluorenyl),(1,1,2,2-tetramethyl-1,2-disilyl-bis-cyclopentadienyl),(1,2-bis(cyclopentadienyl)ethane, and(isopropylidene-cyclopentadienyl-fluorenyl).

Preferred X″ groups are selected from hydride, hydrocarbyl, silyl,germyl, halohydrocarbyl, halosilyl, silyl hydrocarbyl andaminohydrocarbyl groups, or two X″ groups together form a divalentderivative of a conjugated diene or else together they form a neutral,π-bonded, conjugated diene. Most preferred X″ groups are C₁-C₂₀hydrocarbyl groups, including those optionally formed from two X″ groupstogether.

A further class of metal complexes corresponds to the preceding formulaL_(l)MX_(m)X′_(n)X″_(p), or a dimer thereof, wherein X .is a divalentsubstituent of up to 50 non-hydrogen atoms that together with L forms ametallocycle with M.

Preferred divalent X substituents include groups containing up to 30non-hydrogen atoms comprising at least one atom that is oxygen, sulfur,boron or a member of Group 14 of the Periodic Table of the Elementsdirectly attached to the delocalized π-bonded group, and a differentatom, selected from the group consisting of nitrogen, phosphorus, oxygenor sulfur that is covalently bonded to M.

A preferred class of such Group 4 metal coordination complexescorresponds to the formula:

wherein:

M is titanium, zirconium or hafnium in the +2, +3 or +4 formal oxidationstate;

X″ and R³ are as previously defined for formulas AI and AII;

Y is —O—, —S—, —NR*—, —NR*₂—, or —PR*—; and

Z is SiR*₂, CR*₂, SiR*₂SiR*₂, CR*₂CR*₂, CR*═CR*, CR*₂SiR*₂, or GeR*₂,wherein R* is as previously defined.

Illustrative Group 4 metal complexes that are optionally used ascatalysts include:

cyclopentadienyltitaniumtrimethyl, cyclopentadienyltitaniumtriethyl,cyclopentadienyltitaniumtriisopropyl, cyclopentadienyltitaniumtriphenyl,cyclopentadienyltitaniumtribenzyl,cyclopentadienyltitanium-2,4-dimethylpentadienyl,cyclopentadienyltitanium-2,4-dimethylpentadienyltriethylphosphine,cyclopentadienyltitanium-2,4-dimethylpentadienyltrimethylphosphine,cyclopentadienyltitaniumdimethylmethoxide,cyclopentadienyltitaniumdimethylchloride,pentamethylcyclopentadienyltitaniumtrimethyl indenyltitaniumtrimethyl,indenyltitaniumtriethyl, indenyltitaniumtripropyl,indenyltitaniumtriphenyl, tetrahydroindenyltitaniumtribenzyl,pentamethylcyclopentadienyltitaniumtriisopropyl,pentamethylcyclopentadienyltitaniumtribenzyl,pentamethylcyclopentadienyltitaniumdimethylmethoxide,pentamethylcyclopentadienyltitaniumdimethylchloride,bis(η5-2,4-dimethylpentadienyl)titanium,bis(η5-2,4-dimethylpentadienyl)titaniumtrimethylphosphine,bis(η5-2,4-dimethylpentadienyl)titaniumtriethylphosphine,octahydrofluorenyltitaniumtrimethyl, tetrahydroindenyltitaniumtrimethyl,tetrahydrofluorenyltitaniumtrimethyl,(tert-butylamido)(1,1-dimethyl-2,3,4,9,10-1,4,η5,6,7,8-hexahydronaphthalenyl)dimethylsilanetitaniumdimethyl,(tert-butylamido)(1,1,2,3-tetramethyl-2,3,4,9,10-1,4,5,6,7,8-hexahydronaphthalenyl)dImethylsilanetitaniumdimethyl,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethylsilanetitaniumdibenzyl,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethylsilanetitaniumdimethyl,(tert-butylamido)(tetramethyl-,η5-cyclopentadienyl)-1,2-ethanediyltitaniumdimethyl,(tert-butylamido)(tetramethyl-η5-indenyl)dimethylsilanetitaniumdimethyl,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethylsilanetitanium (III) 2-(dimethylamino)benzyl;(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethylsilanetitanium(III) allyl,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethylsilanetitanium(III) 2,4-dimethylpentadienyl,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethyl-silanetitanium(II) 1,4-diphenyl-1,3-butadiene,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethyl-silanetitanium(II) 1,3-pentadiene,(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium (II)1,4-diphenyl-1,3-butadiene,(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium (II)2,4-hexadiene, (tert-butylamido)(2-methylindenyl)dimethylsilanetitanium(IV) 2,3-dimethyl-1,3-butadiene,(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium (IV)isoprene,(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium 1,3-butadiene,(tert-butylamido)(2,3-dimethylinderiyl)dimethylsilanetitanium (IV)2,3-dimethyl-1,3-butadiene,(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium(IV)isoprene;(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium (IV)dimethyl; (tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium(IV) dibenzyl;(tert-butylamido)(2,3dimethylindenyl)dimethylsilanetitanium1,3-butadiene,(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium(11)1,3-pentadiene,(tert-butylamido)(2,3-dimethylindenyl)dimethylsilanetitanium(11)1,4-diphenyl-1,3-butadiene,(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium (11)1,3-pentadiene,(tert-butylamido)(2-methylindenyl)dimethylsilanetitanium(IV) dimethyl, (tert-butylamido)(2-methylindenyl)dimethylsilanetitanium(IV) dibenzyl,(tert-butylamido)(2-methyl4-phenylindenyl)dimethylsilanetitanium (11)1,4-diphenyl-1,3-butadiene,(tert-butylamido)(2-methyl4-phenylindenyl)dimethylsilanetitanium (II)1,3-pentadiene,(tert-butylamido)(2-methyl-4-phenylindenyl)dimethylsilanetitanium (II)2,4-hexadiene,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethyl-silanetitanium1,3-butadiene,(tert-butylamido)(tetramethyl-il5-cyclopentadienyl)dimethyl-silanetitanium(IV) 2,3-dimethyl-1,3-butadiene,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethyl-silanetitanium(IV) isoprene,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethyl-silanetitanium(11) 1,4-dibenzyl-1,3-butadiene,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethyl-silanetitanium(II) 2,4-hexadiene,(tert-butylamido)(tetramethyl-η5-cyclopentadienyl)dimethyl-silanetitanium(II) 3-methyl-1,3-pentadiene,(tert-butylamido)(2,4-dimethylpentadien-3-yl)dimethyl-silanetitaniumclimethyl,(tert-butylamido)(6,6dimethylcyclohexadienyl)dimethyl-silanetitaniumdimethyl,(tert-butylamido)(1,1-dimethyl-2,3,4,9,10,1,4,5,6,7,8-hexahydronaphthalen-4-yl)dimethylsilanetitaniumdimethyl,(tert-butylamido)(1,1,2,3-tetramethyl-2,3,4,9,10,1,4,5,6,7,8-hexahydronaphthalen-4-yl)dimethylsilanetitaniumdimethyl(tert-butylamido)(tetramethyl-η5-cyclopentadienylmethylphenyl-silanetitanium (IV) dimethyl,.(tert-butylamido)(tetramethyl-η5-cyclopentadienylmethylphenyl-silanetitanium (II)1,4-diphenyl-1,3-butadiene,1-(tert-butylamido)-2-(tetramethyl-η5-cyclopentadienyl)ethanediyl-titanium(IV) dimethyl, and1-(tert-butylamido)-2-(tetramethyl-η5-cyclopentadienyl)ethanediyl-titanium(II) 1,4-diphenyl-1,3-butadiene.

Complexes containing two L groups including bridged complexes include:

bis(cyclopentadienyl)zirconiumdimethyl, bis(cyclopentadienyl)zirconiumdibenzyl, bis(cyclopentadienyl)zirconium methyl benzyl,bis(cyclopentadienyl)zirconiummethyl phenyl,bis(cyclopentadienyl)zirconiumdiphenyl,bis(cyclopentadienyl)titanium-allyl,bis(cyclopentadienyl)zirconiummethylmethoxide,bis(cyclopentadienylis(zirconiummethylchloride,bis(pentamethylcyclopentadienyl)zirconiumdimethyl,bis(pentamethylcyclopentadienyl)(titaniumdimethyl,bis(indenyl)zirconiumdlmethyl,bis(indenyl)zirconiummethyl(2-(dimethylamino)benzyl),bis(indenyl)(zirconium methyltrimethylsilyl,bis(tetrahydroindenyl)zirconium methyltrimethylsilyl,bis(pentamethylcyclopentadienyl)zirconiummethyl benzyl,bis(pentamethylcyclopentadienyl)zirconiumdibenzyl,bis(pentamethylcyclopentadienylis(zirconiummethylmethoxide,bis(pentamethylcyclopentadienyl)zirconiummethylchloride,bis(methylethylcyclopentadienyl)zirconiumdimethyl,bis(butylcyclopentadienyl)zirconium dibenzyl,bis(t-butylcyclopentadienyl)zirconiumdimethyl,bis(ethyltetramethylcyclopentadienyl)(zirconiumdimethyl,bis(methylpropylcyclo pentadienyl)zirconium dibenzyl,bis(trimethylsilylcyclopentadienyl)zirconium dibenzyl,dimethylsilyl-bis(cyclopentadienyl)zirconiumdimethyl,dimethylsilyl-bis(tetramethylcyclopentadienyi)titanium-(III)allyldimethylsilyl-bis(t-butylcyclopentadienyl)zirconiumdichloride,dimethylsilyl-bis(n-butylcyclopentadienyl)zirconiumdichloride,(methylene-bis(tetramethylcyclopentadienyl)titanium(III)2-(dimethylamino)benzyl,(methylene-bis(n-butylcyclopentadienyl)titanium(III)2-(dimethylamino)benzyl,dimethylsilyl-bis(indenyl)zirconiumbenzylchloride,dimethylsilyl-bis(2-methylindenyl)zirconiumdimethyl,dimethylsilyl-bis(2-methyl-4-phenylindenyl)zirconiumdimethyl,dimethylsilyl-bis(2-methylindenyl)zirconium-1,4-diphenyl-1,3-butadiene,dimethylsilyl-bis(2-methyl-4-phenylindenyl)zirconium (II)1,4-diphenyl-1,3-butadiene,dimethylsilyl-bis(tetrahydroindenyl)zirconium(ll)1,4-diphenyl-1,3-butadiene,dimethylsilyl-bis(fluorenyl)zirconiummethylchloride,dimethylsilyl-bis(tetrahydrofluorenyl)zirconium bis(trimethylsilyl), anddimethylsilyl. (tetramethylcyclopentadienyl)(fluorenyl)zirconiumdimethyl.

Other catalysts, especially catalysts containing other Group 4 metals,will, of course, be apparent to those skilled in the art.

Preferred metallocene species include constrained geometry metalcomplexes, including titanium complexes, and methods for theirpreparation as are disclosed in U.S. application Ser. No. 545,403, filedJul. 3,1990 (EP-A-416,815); U.S. application Ser. No. 967,365, filedOct. 28, 1992 (EP-A-514,828); and U.S. application Ser. No. 876,268,filed May 1, 1992, (EP-A-520,732), as well as U.S. Pat. Nos. 5,055,438;5,057,475; 5,096,867; 5,064,802; 5,096,867; 5,132,380; 5,132,380;5,470,993; 5,486,632; 5,132,380; and 5,321,106. The teachings of all theforegoing patents, publications and patent applications is herebyincorporated by reference in their entireties.

Metallocene catalysts are advantageously rendered catalytically activeby combination with one or more activating cocatalysts, by use of anactivating technique, or a combination thereof. Advantageous cocatalystsare those boron-containing cocatalysts within the skill in the art.Among the boron-containing cocatalysts are tri(hydrocarbyl)boroncompounds and halogenated derivatives thereof, advantageously havingfrom 1 to about 10 carbons in each hydrocarbyl or halogenatedhydrocarbyl group, more especially perfluorinated tri(aryl)boroncompounds, and most especially tris(pentafluorophenyl)borane), amine,phosphine, aliphatic alcohol and mercaptan adducts of halogenatedtri(C₁-C₁₀ hydrocarbyl)boron compounds, especially such adducts ofperfluorinated tri(aryl)boron compounds. Alternatively, the cocatalystincludes borates such as tetrapheny Borate having as counterionsammonium ions such as are within the skill in the art as illustrated byEuropean Patent EP 672,688 (Canich, Exxon), published Sep. 20, 1995.

The cocatalyst can be used in combination with atri(hydrocarbyl)aluminum compound having from 1 to 10 carbons in eachhydrocarbyl group or an oligomeric or polymeric alumoxane. It ispossible to employ these aluminum compounds for their beneficial abilityto scavenge impurities such as oxygen, water, and aldehydes from thepolymerization mixture. Preferred aluminum compounds include trialkylaluminum compounds having from 2 to 6 carbons in each alkyl group,especially those wherein the alkyl groups are ethyl, propyl, isopropyl,n-butyl, isobutyl, pentyl, neopentyl, or isopentyl, and methylalumoxane,modified by methylalumoxane (that is methylalumoxane modified byreaction with triisobutyl aluminum) (MMAO) and diisobutylalumoxane. Themolar ratio of aluminum compound to metal complex is preferably from1:10,000 to 1000:1, more preferably from 1:5000 to 100:1, mostpreferably from 1:100 to 100:1.

Cocatalysts; are used in amounts and under conditions within the skillin the art. Their use is applicable to all processes within the skill inthe art, including solution, slurry, bulk (especially propylene), andgas phase polymerization processed. Such processes include those fullydisclosed in the references cited previously.

The molar ratio of catalyst/cocatalyst or activator employed preferablyranges from about 1:10,000 to about 100:1, more preferably from about1:5000 to about 10:1, most preferably from about 1:1000 to about 1:1.

When utilizing such strong Lewis acid cocatalysts; to polymerize higher(α-olefins, especially propylene, it has been found especially desirableto also contact the catalyst/cocatalyst mixture with a small quantity ofethylene or hydrogen (preferably at least one mole of ethylene orhydrogen per mole of metal complex, suitably from 1 to 100,000 moles ofethylene or hydrogen per mole of metal complex). This contacting mayoccur before, after or simultaneously to contacting with the higherα-olefin. If the foregoing Lewis acid activated catalyst compositionsare not treated in the foregoing manner, either extremely long inductionperiods are encountered or no polymerization at all results. Theethylene or hydrogen may be used in a suitably small quantity such thatno significant affect on polymer properties is observed.

In most instances, the polymerization advantageously takes place atconditions known in the prior art for Ziegler-Natta or Kaminsky-Sinntype polymerization reactions, i.e., temperatures from 0-250° C. andpressures from atmospheric to 3000 atmospheres. Suspension, solution,slurry, gas phase or high pressure, whether employed in batch orcontinuous form or under other process conditions, including therecycling of condensed monomers or solvent, may be employed if desired.Examples of such processes are well known in the art for example, WO88/02009-A1 or U.S. Pat. No. 5,084,534 (both incorporated herein byreference), disclose conditions that are advantageously employed withthe polymerization catalysts and are incorporated herein by reference intheir entireties. A support, especially silica, alumina, or a polymer(especially polytetrafluoroethylene or a polyolefin) is optionallyemployed, and desirably is employed when the catalysts are used in a gasphase polymerization process. Such supported catalysts areadvantageously not affected by the presence of liquid aliphatic oraromatic hydrocarbons such as are optionally present under the use ofcondensation techniques in a gas phase polymerization process. Methodsfor the preparation of supported catalysts are disclosed in numerousreferences, examples of which are U.S. Pat. Nos. 4,808,561; 4,912,075;5,008,228; 4,914,253; and 5,086,025 (all incorporated herein byreference) and are suitable for the preparation of supported catalysts.

In such a process the reactants and catalysts are optionally added tothe solvent sequentially, in any order, or alternatively one or more ofthe reactants or catalyst system components are premixed with solvent ormaterial preferably miscible therewith then mixed together or into moresolvent optionally containing the other reactants or catalysts. Thepreferred process parameters are dependent on the monomers used and thepolymer desired.

Propylene is added to the reaction vessel in predetermined amounts toachieve predetermined per ratios, advantageously in gaseous form using ajoint mass flow controller. Alternatively propylene or other liquidmonomers are added to the reaction vessel in amounts predetermined toresult in ratios desired in the final product. They are optionally addedtogether with the solvent (if any), alpha-olefin and functionalcomonomer, or alternatively added separately. The pressure in thereactor is a function of the temperature of the reaction mixture and therelative amounts of propylene and/or other monomers used in thereaction. Advantageously, the polymerization process is carried out at apressure of from about 10 to about 1000 psi (70 to 7000 kPa), mostpreferably from about 140 to about 550 psi (980 to 3790 kPa). Thepolymerization is then conducted at a temperature of from 25 to 200° C.,preferably from 50 to 100° C., and most preferably from 60 to 80° C.

The process is advantageously continuous, in which case the reactantsare added continuously or at intervals and the catalyst and, optionallycocatalyst, are added as needed to maintain reaction or make up loss orboth.

Solution polymerization or bulk polymerization is preferred. In thelatter case liquid polypropylene is the reaction medium. Preferredsolvents include mineral oils and the various hydrocarbons which areliquid at reaction temperatures. Illustrative examples of usefulsolvents include straight- and branched-chain hydrocarbons such asalkanes, e.g. isobutane, butane, pentane, isopentene, hexane, heptane,octane and nonane, as well as mixtures of alkanes including kerosene andIsopar E, available from Exxon Chemicals Inc.; cyclic and alicyclichydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane,methylcycloheptane, and mixtures thereof; and aromatics andalkyl-substituted aromatic compounds such as benzene, toluene, xylenes,ethylbenzene, diethylbenzene, and the like; and perfluorinatedhydrocarbons such as perfluorinated C₄-C₁₀ alkanes. Suitable solventsmay include liquid olefins which may act as monomers or comonomers.Mixtures of the foregoing are also suitable.

At all times, the individual ingredients as well as the recoveredcatalyst components are protected from oxygen and moisture. Therefore,the catalyst components and catalysts are prepared and recovered in anoxygen- and moisture-free atmosphere. Preferably, therefore, thereactions are performed in the presence of a dry, inert gas such as, forexample, nitrogen.

Without limiting in any way the scope of the invention, one means forcarrying out such a polymerization process is as follows. In astirred-tank reactor, olefin monomer is introduced continuously togetherwith solvent and polyene monomer. The reactor contains a liquid phasecomposed substantially of monomers together with any solvent oradditional diluent. Catalyst and cocatalyst are continuously introducedin the reactor liquid phase. The reactor temperature and pressure may becontrolled by adjusting the solvent/monomer ratio, the catalyst additionrate, as well as by cooling or heating coils, jackets or both. Thepolymerization rate is controlled by the rate of catalyst addition. Thepolymer product molecular weight is controlled, optionally; bycontrolling other polymerization variables such as the temperature,monomer concentration, or by a stream of hydrogen introduced to thereactor, as is well known in the art. The reactor effluent is contactedwith a catalyst kill agent such as water or an alcohol. The polymersolution is optionally heated, and the polymer product is recovered byflashing off gaseous monomers as well as residual solvent or diluent atreduced pressure, and, if necessary, conducting further devolatilizationin equipment such as a devolatilizing extruder. In a continuous process,the mean residence time of the catalyst and polymer in the reactorgenerally is from about 5 minutes to 8 hours, and preferably from 10minutes to 6 hours.

Preferably, the polymerization is conducted in a continuous solutionpolymerization system, optionally comprising more than one reactorconnected in series or parallel.

The ethylene polymer used in the polymer blend composition to make thefiber and fabric of the present invention is characterized as having ahigh molecular weight. Suitable ethylene polymers include, for example,high density polyethylene (HDPE), heterogeneously branched linear lowdensity polyethylene (LLDPE), heterogeneously branched ultra low densitypolyethylene (ULDPE), homogeneously branched linear ethylene polymers,homogeneously branched substantially linear ethylene polymers,homogeneously branched long chain branched ethylene polymers, andethylene vinyl or vinylidene aromatic monomer interpolymers. Buthomogeneously branched ethylene polymers and ethylene vinyl orvinylidene aromatic monomer interpolymers are preferred, andhomogeneously branched substantially linear ethylene polymers andsubstantially random ethylene/vinyl aromatic interpolymers are mostpreferred.

The homogeneously branched substantially linear ethylene polymers usedin the polymer blend compositions disclosed herein can be interpolymersof ethylene with at least one C₃-C₂₀ α-olefin. The term “Interpolymer”and “ethylene polymer” used herein indicates that the polymer can be acopolymer, a terpolymer. Monomers usefully copolymerized with ethyleneto make the homogeneously branched linear or substantially linearethylene polymers include the C₃-C₂₀ α-olefins especially 1-pentene,1-hexene, 4-methyl-1-pentene, and 1-octene. Especially preferredcomonomers include 1-pentene, 1-hexene and 1-octene. Copolymers ofethylene and a C₃-C₂₀ α-olefin are especially preferred.

The term “substantially linear” means that the polymer backbone issubstituted with 0.01 long chain branches/1000 carbons to 3 long chainbranches/1000 carbons, more preferably from 0.01 long chainbranches/1000 carbons to 1 long chain branches/1000 carbons, andespecially from 0.05 long chain branches/1000 carbons to 1 long chainbranches/1000 carbons.

Long chain branching is defined herein as a branch having a chain lengthgreater than that of any short chain branches which are a result ofcomonomer incorporation. The long chain branch can be as long as aboutthe same length as the length of the polymer back-bone.

Long chain branching can be determined by using ¹³C nuclear magneticresonance (NMR) spectroscopy and is quantified using the method ofRandall (Rev. Macromol. Chem. Phys., C29 (2&3), p. 275-287), thedisclosure of which is incorporated herein by reference.

In the case of substantially linear ethylene polymers, such polymers canbe characterized as having:

a) a melt flow ratio, I₁₀/I₂, ≧5.63,

b) a molecular weight distribution, M_(w)/M_(n) , defined by theequation:

Mw/Mn≦(I₁₀/I₂)−4.63,

and

c) a critical shear stress at onset of gross melt fracture greater than4×10⁶ dynes/cm² or a critical shear rate at onset of surface meltfracture at least 50 percent greater than the critical shear rate at theonset of surface melt fracture of either a homogeneously orheterogeneously branched linear ethylene polymer having about the sameI₂ and M_(w)/M_(n) or both.

In contrast to substantially linear ethylene polymers, linear ethylenepolymers lack long chain branching, i.e., they have less than 0.01 longchain branches/1000 carbons. The term “linear ethylene polymers” thusdoes not refer to high pressure branched polyethylene, ethylene/vinylacetate copolymers, or ethylene/vinyl alcohol copolymers which are knownto those skilled in the art to have numerous long chain branches.

Linear ethylene polymers include, for example, the traditionalheterogeneously branched linear low density polyethylene polymers orlinear high density polyethylene polymers made using Zieglerpolymerization processes (e.g., U.S. Pat. No. 4,076,698 (Anderson etal.)) the disclosure of which is incorporated herein by reference), orhomogeneous linear polymers (e.g., U.S. Pat. No. 3,645,992 (Elston) thedisclosure of which is incorporated herein by reference).

Both the homogeneous linear and the substantially linear ethylenepolymers used to form the fibers have homogeneous branchingdistributions. The term “homogeneously branching distribution” meansthat the comonomer is randomly distributed within a given molecule andthat substantially all of the copolymer molecules have the sameethylene/comonomer ratio. The homogeneous ethylene/x-olefin polymersused in this invention essentially lack a measurable “high density”fraction as measured by the TREF technique (i.e., the homogeneousbranched ethylene/α-olefin polymers are characterized as typicallyhaving less than 15 weight percent, preferably less than 10 weightpercent, and more preferably less than 5 weight percent of a polymerfraction with a degree of branching less than or equal to 2 methyls/1000carbons).

The homogeneity of the branching distribution can be measured variously,including measuring the SCBDI (Short Chain Branch Distribution Index) orCDBI (Composition Distribution Branch Index). SCBDI or CDBI is definedas the weight percent of the polymer molecules having a comonomercontent within 50 percent of the median total molar comonomer content.The CDBI of a polymer is readily calculated from data obtained fromtechniques known in the art, such as, for example, temperature risingelusion fractionation (abbreviated herein as “TREF)as described, forexample, in Wild et al, Journal of Polymer Science, Poly. Phys. Ed.,Vol. 20, p. 441 (1982), U.S. Pat. No. 5,008,204 (Stehling), thedisclosure of which is incorporated herein by reference. The techniquefor calculating CDBI is described in U.S. Pat. No. 5,322,728 (Davey etal.) and in U.S. Pat. No. 5,246,783 (Spenadel et al.), both disclosuresof which are incorporated herein by reference. The SCBDI or CDBI forhomogeneously branched linear and substantially linear ethylene polymersis typically greater than 30 percent, and is preferably greater than 50percent, more preferably greater than 60 percent, even more preferablygreater than 70 percent, and most preferably greater than 90 percent.

The homogeneous branched ethylene polymers used to make the fibers ofthe present invention will preferably have a single melting peak, asmeasured using differential scanning calorimetry (DSC), in contrast toheterogeneously branched linear ethylene polymers, which have 2 or moremelting peaks, due to the heterogeneously branched polymer's broadbranching distribution.

Substantially linear ethylene polymers exhibit a highly unexpected flowproperty where the I_(10/I) ₂ value of the polymer is essentiallyindependent of polydispersity index (i.e., M_(w)/M_(n)) of the polymer.This is contrasted with conventional homogeneous linear ethylenepolymers and heterogeneously branched linear polyethylene resins forwhich one must increase the polydispersity index in order to increasethe I_(10/I) ₂ value. Substantially linear ethylene polymers alsoexhibit good processability and low pressure drop through a spinneretpack, even when using high shear filtration.

Homogeneous linear ethylene polymers useful to make the fibers andfabrics of the invention are a known class of polymers which have alinear polymer backbone, no long chain branching and a narrow molecularweight distribution. Such polymers are interpolymers of ethylene and atleast one α-olefin comonomer of from 3 to 20 carbon atoms, and arepreferably copolymers of ethylene with a C₃-C₂₀ α-olefin, and are mostpreferably copolymers of ethylene with propylene, 1-butene, 1-hexene,4-methyl-1-pentene or 1-octene. This class of polymers is disclosed forexample, by Elston in U.S. Pat. No. 3,645,992 and subsequent processesto produce such polymers using metallocene catalysts have beendeveloped, as shown, for example, in EP 0 129 368, EP 0 260 999, U.S.Pat. Nos. 4,701,432; 4,937,301; 4,935,397; 5,055,438; and WO 90/07526,and others. The polymers can be made by. conventional polymerizationprocesses (e.g., gas phase, slurry, solution, and high pressure).

Another measurement useful in characterizing the molecular weight ofethylene polymers is conveniently indicated using a melt indexmeasurement. according to ASTM D-1238, Condition 190° C./10 kg (formerlyknown as “Condition (N)” and also known as I₁₀). The ratio of these twomelt index terms is the melt flow ratio and is designated as I_(10/I) ₂.For the substantially linear ethylene polymers used polymer compositionsuseful in making the fibers of the invention, the I_(10/I) ₂ ratioindicates the degree of long chain branching, i.e., the higher theI_(10/I) ₂ ratio, the more long chain branching in the polymer. Thesubstantially linear ethylene polymers can have varying I_(10/I) ₂ratios, while maintaining a low molecular weight distribution (i.e.,M_(w)/M_(n) from 1.5 to 2.5). Generally, the I_(10/I) ₂ ratio of thesubstantially linear ethylene polymers is at least 5.63, preferably atleast 6, more preferably at least 7, and especially at least 8.Generally, the upper limit of I₁₀/I₂ ratio for the homogeneouslybranched substantially linear ethylene polymers is 50 or less,preferably 30 or less, and especially 20 or less.

Additives such as antioxidants (e.g., hindered phenolics (e.g.,Irganox™1010 made by Ciba-Geigy Corp.), phosphites (e.g., Irgafos™) 168made by Ciba-Geigy Corp.), cling additives (e.g., polyisobutylene(PIB)), antiblock additives, pigments, can also be included in the firstpolymer, the second polymer, or the overall polymer composition usefulto make the fibers and fabrics of the invention, to the extent that theydo not interfere with the enhanced fiber and fabric propertiesdiscovered by Applicants.

The molecular weight distributions of ethylene polymers are determinedby gel permeation chromatography (GPC) on a Waters 150° C. hightemperature chromatographic unit equipped with a differentialrefractometer and three columns of mixed porosity. The columns aresupplied by Polymer Laboratories and are commonly packed with pore sizesof 10³, 10⁴, 10⁵ and 10⁶ Å. The solvent is 1,2,4-trichlorobenzene, fromwhich about 0.3 percent by weight solutions of the samples are preparedfor injection. The flow rate is about 1.0 milliliters/minute, unitoperating temperature is about 140° C. and the injection size is about100 microliters.

The molecular weight determination with respect to the polymer backboneis deduced by using narrow molecular weight distribution polystyrenestandards (from Polymer Laboratories) in conjunction with their elutionvolumes. The equivalent polyethylene molecular weights are determined byusing appropriate Mark-Houwink coefficients for polyethylene andpolystyrene (as described by Williams and Ward in Journal of PolymerScience Polymer Letters, Vol. 6, p. 621, 1968) to derive the followingequation:

M_(polyethylene) =a*(M_(polystyrene))^(b).

In this equation, a=0.4316 and b=1.0. Weight average molecular weight,Mw, is calculated in the usual manner according to the followingformula: M_(j)=(Σw_(i)(M_(i) ^(j))^(j); where w_(i) is the weightfraction of the molecules with molecular weight M_(i) eluting from theGPC column in fraction i and j=1 when calculating _(Mw), and j=−1 whencalculating M_(n). The novel composition has M_(w)/M_(n) less than orequal to 3.3, preferably less than or equal to 3, and especially in therange of from about 2.4 to about 3.

The M_(w)/M_(n) of the substantially linear homogeneously branchedethylene polymers is defined by the equation:

M_(w)/M_(n)≦(I₁₀/I₂)−4.63

Preferably, the Mw/Mn for the ethylene polymers is from 1.5 to 2.5, andespecially from 1.8 to 2.2.

An apparent shear stress versus apparent shear rate plot is used toidentify the melt fracture phenomena. According to Ramamurthy in Journalof Rheology. 30(2), 337-357, 1986, above a certain critical flow rate,the observed extrudate irregularities may be broadly classified into twomain types: surface melt fracture and gross melt fracture.

Surface melt fracture occurs under apparently steady flow conditions andranges in detail from loss of specular gloss to the more severe form of“sharkskin”. In this disclosure, the onset of surface melt fracture ischaracterized at the beginning of losing extrudate gloss at which thesurface roughness of extrudate can only be detected by 40×magnification. The critical shear rate at onset of surface melt fracturefor a substantially linear ethylene polymer is at least 50 percentgreater than the critical shear rate at the onset of surface meltfracture of a homogeneous linear ethylene polymer having the same I₂ andM_(w)/M_(n).

Gross melt fracture occurs at unsteady flow conditions and ranges indetail from regular (alternating rough and smooth, helical, etc.) torandom distortions. For commercial acceptability, (e.g., in blown filmproducts), surface defects should be minimal, if not absent. Thecritical shear rate at onset of surface melt fracture (OSMF) and onsetof gross melt fracture (OGMF) will be used herein based on the changesof surface roughness and configurations of the extrudates extruded by aGER.

The gas extrusion rheometer is described by M. Shida, R. N. Shroff andL. V. Cando in Polymer Engineering Science, Vol.17, no. 11, p. 770(1977), and in Rheometers for Molten Plastics by John Dealy, publishedby Van Nostrand Reinhold Co. (1982) on page 97, both publications ofwhich are incorporated by reference herein in their entirety. AII GERexperiments are performed at a temperature of 190° C., at nitrogenpressures between 5250 to 500 psig using a 0.0296 inch diameter, 20:1L/D die. An apparent shear stress vs. apparent shear rate plot is usedto identify the melt fracture phenomena. According to Ramamurthy inJournal of Rheology, 30(2), pp. 337-357, 1986, above a certain criticalflow rate, the observed extrudate irregularities may be broadlyclassified into two main types: surface melt fracture and gross meltfracture.

For the polymers described herein, the PI is the apparent viscosity (inKpoise) of a material measured by GER at a temperature of 190° C., atnitrogen pressure of 2500 psig using a 0.0296 inch diameter, 20:1 L/Ddie, or corresponding apparent shear stress of 2.15×10⁶ dyne/cm².

The processing index is measured at a temperature of 190° C., atnitrogen pressure of 2500 psig using 0.0296 inch diameter, 20:1 L/D diehaving an entrance angle of 180°.

Exemplary constrained geometry catalysts for use in polymerizing thehomogeneously branched substantially linear ethylene polymerspreferentially used to make the novel fibers and other articles of thepresent invention preferably include those constrained geometrycatalysts as disclosed in U.S. application Ser. No.: 545,403, filed Jul.3, 1990; Ser. No. 758,654, now U.S. Pat. No. 5,132,380; Ser. No.758,660, now abandoned, filed Sep. 12, 1991; and Ser. No. 720,041, nowabandoned, filed Jun. 24, 1991, and in U.S. Pat. Nos. 5,272,236 and5,278,272, the disclosures of all of which are incorporated herein byreference.

As indicated above, substantially random ethylene/vinyl aromaticinterpolymers are especially preferred ethylene. polymers for use in thepresent invention. Representative of substantially random ethylene/vinylaromatic interpolymers are substantially random ethylene/styreneinterpolymers preferably containing at least 20, more preferably equalto or greater than 30, and most preferably equal to or greater than 50weight percent interpolymerized styrene monomer.

A substantially random interpolymer comprises in polymerized form i) oneor more α-olefin monomers and ii) one or more vinyl or vinylidenearomatic monomers and/or one or more sterically hindered aliphatic orcycloaliphatic vinyl or vinylidene monomers, and optionally iii) otherpolymerizable ethylenically unsaturated monomer(s).

The term “interpolymer” is used herein to indicate a polymer wherein atleast two different monomers are polymerized to make the interpolymer.

The term “substantially random” in the substantially random interpolymerresulting from polymerizing i) one or more α-olefin monomers and ii) oneor more vinyl or vinylidene aromatic monomers and/or one or moresterically hindered aliphatic or cycloaliphatic vinyl or vinylidenemonomers, and optionally iii) other polymerizable ethylenicallyunsaturated monomer(s) as used herein generally means that thedistribution of the monomers of said interpolymer can be described bythe Bernoulli statistical model or by a first or second order Markovianstatistical model, as described by J. C. Randall in Polymer SequenceDetermination, Carbon-13 NMR Method, Academic Press New York, 1977, pp.71-78. Preferably, the substantially random interpolymer resulting frompolymerizing one or more α-olefin monomers and one or more vinyl orvinylidene aromatic monomers, and optionally other polymerizableethylenically unsaturated monomer(s), does not contain more than 15percent of the total amount of vinyl or vinylidene aromatic monomer inblocks of vinyl or vinylidene aromatic monomer of more than 3 units.More preferably, the interpolymer is not characterized by a high degreeof either isotacticity or syndiotacticity. This means that in thecarbon-13 NMR spectrum of the substantially random interpolymer, thepeak areas corresponding to the main chain methylene and methine carbonsrepresenting either meso diad sequences or racemic diad sequences shouldnot:exceed 75 percent of the total peak area of the a main chainmethylene and methine carbons.

By the subsequently used terre “substantially random interpolymer” it ismeant a substantially random interpolymer produced from theabove-mentioned monomers.

Suitable α-olefin monomers which are useful for preparing thesubstantially random interpolymer include, for example, α-olefinmonomers containing from 2 to 20, preferably from 2 to 12, morepreferably from 2 to 8 carbon atoms. Preferred such monomers includeethylene, propylene, butene-1,4-methyl-1-pentene, hexene-1 and octene-1.Most preferred are ethylene or a combination of ethylene with C₃-C₈α-olefins. These α-olefins do not contain an aromatic moiety.

Suitable vinyl or vinylidene aromatic monomers which can be employed toprepare the substantially random interpolymer include, for example,those represented by the following formula I

wherein R¹ is selected from the group of radicals consisting of hydrogenand alkyl radicals containing from 1 to 4 carbon atoms, preferablyhydrogen or methyl; each R² is independently selected from the group ofradicals consisting of hydrogen and alkyl radicals containing from 1 to4 carbon atoms, preferably hydrogen or methyl; Ar is a phenyl group or aphenyl group substituted with from 1 to 5 substituents; selected fromthe group consisting of halo, C₁-C₄-alkyl, and C₁-C₄-haloalkyl; and nhas a value from zero to 4, preferably from zero to 2, most preferablyzero. Particularly suitable such monomers include styrene and loweralkyl- or halogen-substituted derivatives thereof. Exemplary monovinylor monovinylidene aromatic monomers include styrene, vinyl toluene,α-methylstyrene, t-butyl styrene or chlorostyrene, including all isomersof these compounds. Preferred monomers include styrene, α-methylstyrene, the lower alkyl-(C₁-C₄) or phenyl-ring substituted derivativesof styrene, such as for example, ortho-, meta-, and para-methylstyrene,the ring halogenated styrenes, para-vinyl toluene or mixtures thereof. Amore preferred aromatic monovinyl monomer is styrene.

By the term “sterically hindered aliphatic or cycloaliphatic vinyl orvinylidene monomers”, it is meant addition polymerizable vinyl orvinylidene monomers corresponding to the formula:

wherein A¹ is a sterically bulky, aliphatic or cycloaliphaticsubstituent of up to 20 carbons, R¹ is selected from the group ofradicals consisting of hydrogen and alkyl radicals containing from 1 to4 carbon atoms, preferably hydrogen or methyl; each R² is independentlyselected from the group of radicals consisting of hydrogen and alkylradicals containing from 1 to 4 carbon atoms, preferably hydrogen ormethyl; or alternatively R¹ and A¹ together form a ring system.

By the term “sterically bulky” is meant that the monomer bearing thissubstituent is normally incapable of addition polymerization by standardZiegler-Natta polymerization catalysts at a rate comparable withethylene polymerizations.

α-Olefin monomers containing from 2 to about 20 carbon atoms and havinga linear aliphatic structure such as propylene, butene-1, hexene-1 andoctene-1 are not considered as sterically hindered aliphatic monomers.Preferred sterically hindered aliphatic or cycloaliphatic vinyl orvinylidene compounds are monomers in which one of the carbon atomsbearing ethylenic unsaturation is tertiary or quaternary substituted.Examples of such substituents include cyclic aliphatic groups such ascyclohexyl, cyclohexenyl, cyclooctenyl, or ring alkyl or arylsubstituted derivatives thereof, tert-butyl or norbornyl. Most preferredsterically hindered aliphatic or cycloaliphatic vinyl or vinylidenecompounds are the various isomeric vinyl-ring substituted derivatives ofcyclohexene and substituted cyclohexenes, and 5-ethylidene-2-norbornene.Especially suitable are 1-, 3-, and 4-vinylcyclohexene.

The substantially random interpolymers usually contain from about 0.5 toabout 65, preferably from about 1 to about 55, more preferably fromabout 2 to about 50 mole percent of at least one vinyl or vinylidenearomatic monomer and/or sterically hindered aliphatic or cycloaliphaticvinyl or vinylidene monomer and from about 35 to about 99.5, preferablyfrom about 45 to about 99, more preferably from about 50 to about 98mole percent of at least one aliphatic α-olefin having from about 2 toabout 20 carbon atoms.

Other optional polymerizable ethylenically unsaturated monomer(s)include strained ring olefins such as norbornene and C₁-C₁₀-alkyl orC₈-C₁₀-aryl substituted norbornenes, with an exemplary substantiallyrandom interpolymer being ethylene/styrene/norbornene.

The most preferred substantially random interpolymers are interpolymersof ethylene and styrene and interpolymers of ethylene, styrene and atleast one α-olefin containing from 3 to 8 carbon atoms.

The number average molecular weight (M_(n)) of the substantially randominterpolymers is usually greater than 5,000, preferably from about20,000 to about 1,000,000, more preferably from about 50,000 to about500,000. The glass transition temperature (T_(g)) of the substantiallyrandom interpolymers is preferably from about −40° C. to about +35° C.,preferably from about 0° C. to about +30° C., most preferably from about+10° C. to about +25° C., measured according to differential mechanicalscanning (DMS).

The substantially random interpolymers may be modified by typicalgrafting, hydrogenation, functionalizing, or other reactions well knownto those skilled in the art. The polymers may be readily sulfonated orchlorinated to provide functionalized derivatives according toestablished techniques. The substantially random interpolymers may alsobe modified by various chain extending or crosslinking processesincluding, but not limited to peroxide-, silane-, sulfur-, radiation-,or azide-based cure systems. A full description of the variouscrosslinking technologies is described in copending U.S. patentapplication Ser. Nos. 08/921,641 and 08/921,642, both filed on Aug. 27,1997, the entire contents of both of which are herein incorporated byreference.

Dual cure systems, which use a combination of heat, moisture cure, andradiation steps, may also be effectively employed. Dual cure systems aredisclosed and claimed in U.S. patent application Ser. No. 536,022, filedon Sep. 29, 1995, in the names of K. L. Walton and S. V. Karande,incorporated herein by reference. For instance, it may be desirable toemploy peroxide crosslinking agents in conjunction with silanecrosslinking agents, peroxide crosslinking agents in conjunction withradiation, sulfur-containing crosslinking agents in conjunction withsilane crosslinking agents, etc.

The substantially random interpolymers may also be modified by variouscrosslinking processes including, but not limited to the incorporationof a diene component as a termonomer in its preparation and subsequentcrosslinking by the aforementioned methods and further methods includingvulcanization via the vinyl group using sulfur for example as the crosslinking agent.

One suitable method for manufacturing substantially randomethylene/vinyl aromatic interpolymers includes polymerizing a mixture ofpolymerizable monomers in the presence of one or more metallocene orconstrained geometry catalysts in combination with various cocatalysts,as described in EP-A-0,416,815 by James C. Stevens et al. and U.S. Pat.No. 5,703,187 by Francis J. Timmers, both of which are incorporatedherein by reference in their entirety. Preferred operating conditionsfor such polymerization reactions include pressures from atmospheric upto 3000 atmospheres and temperatures from −300° C. to 200° C.Polymerizations and unreacted monomer removal at temperatures above theauto-polymerization temperature of the respective monomers may result information of some amounts of homopolymer polymerization productsresulting from free radical polymerization.

Examples of suitable catalysts and methods for preparing thesubstantially random interpolymers are disclosed in U.S. applicationSer. No. 702,475, filed May 20, 1991 (EP-A-514,828); as well as U.S.Pat. Nos.: 5,055,438; 5,057,475; 5,096,867; 5,064,802; 5,132,380;5,189,192; 5,321,106; 5,347,024; 5,350,723; 5,374,696; 5,399,635;5,470,993; 5,703,187; and 5,721,185, all of which patents andapplications are incorporated herein by reference.

The substantially random ethylene/vinyl aromatic interpolymers can alsobe prepared by the methods described in JP 07/278230 (the disclosure ofwhich is incorporated herein by reference) employing compounds shown bythe general formula

Where Cp¹ and Cp² are cyclopentadienyl groups, indenyl groups, fluorenylgroups, or substituents of these, independently of each other; R¹ and R²are hydrogen atoms, halogen atoms, hydrocarbon groups with carbonnumbers of 1-12, alkoxyl groups, or aryloxyl groups, independently ofeach other; M is a group IV metal, preferably Zr or Hf, most preferablyZr; and R³ is an alkylene group or silanediyl group used to crosslinkCp¹ and Cp².

The substantially random ethylene/vinyl aromatic interpolymers can alsobe prepared by the methods described by John G. Bradfute et al. (W. R.Grace & Co.) in WO 95/32095; by R. B. Pannell (Exxon Chemical Patents,inc.) in WO 94/00500; and in Plastics Technology p. 25 (September 1992),all of which are incorporated herein by reference in their entirety.

Also suitable are the substantially random interpolymers which compriseat least one α-olefin/vinyl aromatic/vinyl aromatic/α-olefin tetraddisclosed in U.S. application Ser. No. 08/708,869, filed Sep. 4, 1996,and WO 98/09999, both by Francis J. Timmers et al. These interpolymerscontain additional signals in their carbon-13 NMR spectra withintensities greater than three times the peak to peak noise. Thesesignals appear in the chemical shift range 43.70-44.25 ppm and 38.0-38.5ppm. Specifically, major peaks are observed at 44.1, 43.9, and 38.2 ppm.A proton test NMR experiment indicates that the signals in the chemicalshift region 43.70-44.25 ppm are methine carbons and the signals in theregion 38.0-38.5 ppm are methylene carbons.

It is believed that these new signals are due to sequences involving twohead-to-tail vinyl aromatic monomer insertions preceded and followed byat least one α-olefin insertion, e.g. anethylene/styrene/styrene/ethylene tetrad wherein the styrene monomerinsertions of said tetrads occur exclusively in a 1,2 (head to tail)manner. It is understood by one skilled in the art that for such tetradsinvolving a vinyl aromatic monomer other than styrene and an α-olefinother than ethylene that the ethylene/vinyl aromatic monomer/vinylaromatic monomer/ethylene tetrad will give rise to similar carbon-13 NMRpeaks but with slightly different chemical shifts.

These interpolymers can be prepared by conducting the polymerization attemperatures of from about −30° C. to about 250° C. in the presence ofsuch catalysts as those represented by the formula:

wherein each Cp is independently, each occurrence, a substitutedcyclopentadienyl group n-bound to M; E is C or Si; M is a group IVmetal, preferably Zr or Hf, most preferably Zr; each R is independently,each occurrence, H, hydrocarbyl, silahydrocarbyl, or hydrocarbylsilyl,containing up to 30, preferably from about 1 to about 20, morepreferably from about 1 to about 10 carbon or silicon atoms; each R′ isindependently, each occurrence, H, halo, hydrocarbyl, hyrocarbyloxy,silahydrocarbyl, hydrocarbylsilyl containing up to 30, preferably fromabout 1 to about 20, more preferably from about 1 to about 10 carbon orsilicon atoms or two R′ groups together can be a C₁-C₁₀ hydrocarbylsubstituted 1,3-butadiene; M is 1 or 2; and optionally, but preferablyin the presence of an activating cocatalyst.

Particularly, suitable substituted cyclopentadienyl groups include thoseillustrated by the formula:

wherein each R is independently, each occurrence, H, hydrocarbyl,silahydrocarbyl, or hydrocarbylsilyl, containing up to 30, preferablyfrom about 1 to about 20, more preferably from about 1 to about 10carbon or silicon atoms or two R groups together form a divalentderivative of such group. Preferably, R independently each occurrence is(including where appropriate all isomers) hydrogen, methyl, ethyl,propyl, butyl, pentyl, hexyl, benzyl, phenyl or silyl or (whereappropriate) two such R groups are linked together forming a fused ringsystem such as indenyl, fluorenyl, tetrahydroindenyl,tetrahydrofluorenyl, or octahydrofluorenyl.

Particularly preferred catalysts include, for example,racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconiumdichloride,racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconium1,4diphenyl-1,3-butadiene,racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconiumdi-C₁-C₄ alkyl,racemic-(dimethylsilanediyl)-bis-(2-methyl4-phenylindenyl)zirconiumdi-C₁-C₄ alkoxide, or any combination thereof and the like.

It is also possible to use the following titanium-based constrainedgeometry catalysts,[n-(1,1-dimethylethyl)-1,1-dimethyl-1-[(1,2,3,4,5-η)-1,5,6,7-tetrahydro-s-indacen-1-yl]silanaminato(2-)-n]titaniumdimethyl; (1-indenyl)(tert-butylamido)dimethyl-silane titanium dimethyl;((3-tert-butyl)(1,2,3,4,5-η)-1-indenyl)(tert-butylamido)dimethylsilanetitanium dimethyl; and((3-iso-propyl)(1,2,3,4,5-η)-1-indenyl)(tert-butyl amido)dimethylsilanetitanium dimethyl, or any combination thereof and the like.

Further preparative methods for the interpolymers used in the presentinvention have been described in the literature. Longo and Grassi(Makromol. Chem. Volume 191, pages 2387 to 2396 [1990]) and D'Annielloet al. (Journal of Applied Polymer Science, Volume 58, pages 1701-1706[1995]) reported the use of a catalytic system based on methylalurnoxane(MAO) and cyclopentadienyl-titanium trichloride (CpTiCl₃) to prepare anethylene-styrene copolymer. Xu and Lin (Polymer Preprints Am. Chem.Soc., Div. Polym. Chem.), Volume 35, pages 686,687 [1994]) have reportedcopolymerization using a MgCl₂TiCl₄/NdCl₃/Al(iBu)₃ catalyst to giverandom copolymers of styrene and propylene. Lu et al (Journal of AppliedPolymer Science, Volume 53, pages 1453 to 1460 [1994]) have describedthe copolymerization of ethylene and styrene using a TiCl₄/NdCl₃/MgCl₂/al(Et)₃ catalyst. Sernetz and Mulhaupt, (Macromol. Chem. Phys., V. 197,pp. 1071-1083, 1997) have described the influence of polymerizationconditions on the copolymerization of styrene with ethylene usingMe₂Si(Me₄Cp)(n-tert-butyl)TiCl₂/Methylaluminoxane Ziegler-Nattacatalysts. Copolymers of ethylene and styrene produced by bridgedmetallocene catalysts have been described by Arai, Toshiaki and Suzuki(Polymer Preprints Am. Chem. Soc. Div. Polym. Chem.), Volume 38, pages349, 350 [1997]) and in U.S. Pat. No. 5,652,315, issued to Mitsui ToatsuChemicals, Inc. The manufacture of α-olefin/vinyl aromatic monomerinterpolymers such as propylene/styrene and butene/styrene are describedin U.S. Pat. No. 5,244,996, issued to Mitsui Petrochemical IndustriesLtd. or U.S. Pat. No. 5,652,315 also issued to Mitsui PetrochemicalIndustries Ltd. or as disclosed in DE 197 11339 A1 to Denki Kagaku KogyoKK. All of the above disclosures of methods for preparing theinterpolymer component are incorporated herein by reference. Also,although of high isotacticity and therefore not “substantially random”,the random copolymers of ethylene and styrene as disclosed in PolymerPreprints, Vol. 39, no. 1, March 1998 by Toru Aria et al. (thedisclosure of which is incorporated herein by reference) can also beemployed as the ethylene polymer of the present invention.

While preparing the substantially random interpolymer, an amount ofatactic vinyl aromatic homopolymer may be formed due tohomopolymerization of the vinyl aromatic monomer at elevatedtemperatures. The presence of vinyl aromatic homopolymer is in generalnot detrimental for the purposes of the present invention and can betolerated. The vinyl aromatic homopolymer may be separated from theinterpolymer, if desired, by extraction techniques such as selectiveprecipitation from solution with a non-solvent for either theinterpolymer or the vinyl aromatic homopolymer. Nevertheless, for thepurpose of the present invention, it is preferred that no more than 30weight percent, preferably less than 20 weight percent (based on thetotal weight of the interpolymers) of atactic vinyl aromatic homopolymerbe is present.

The polypropylene and ethylene polymers may be produced via a continuous(as opposed to a batch) controlled polymerization process using at leastone reactor for each polymer. But the inventive polymer blendcomposition itself (or a blend comprising or constituting thepolypropylene polymer and/or a separate blend comprising or constitutingthe ethylene polymer) can also be produced using multiple reactors(e.g., using a multiple reactor configuration as described in U.S. Pat.No. 3;914,342 (Mitchell), incorporated herein by reference), with thepolypropylene polymer being manufactured in one reactor and the ethylenepolymer being manufactured in at least one other reactor. The multiplereactors can be operated in series or in parallel, with at least oneconstrained geometry catalyst employed in at least one of the reactorsat a polymerization temperature and pressure sufficient to produce thepolypropylene polymer and/or the ethylene polymer having the desiredproperties.

According to a preferred embodiment of the present process, the polymersare produced in a continuous process, as opposed to a batch process.Preferably, the ethylene polymerization or interpolymerizationtemperature is from 20° C. to 250° C., using constrained geometrycatalyst technology. If a narrow molecular weight distribution polymer(M_(w)M_(n) of from 1.5 to 2.5) having a higher l₁₀/I₂ ratio (e.g.,I₁₀/I₂ of 7 or more, preferably at least 8, especially at least 9) isdesired, the ethylene concentration in the reactor is preferably notmore than 8 percent by weight of the reactor contents, especially notmore than 4 percent by weight of the reactor contents. Preferably, thepolymerization is performed in a solution polymerization process.Generally, manipulation of I₁₀/I₂ while holding M_(w)/M_(n) relativelylow for producing the substantially linear polymers described herein isa function of reactor temperature and/or ethylene concentration. Reducedethylene concentration and higher temperature generally produces higherI₁₀/I₂.

The polymerization conditions for manufacturing the homogeneous linearor substantially linear ethylene polymers used to make the fibers of thepresent invention are generally those useful in the solutionpolymerization process, although the application of the presentinvention is not limited thereto. Slurry and gas phase polymerizationprocesses are also believed to be useful, provided the proper catalystsand polymerization conditions are employed.

One technique for polymerizing the homogeneous linear ethylene polymersuseful herein is disclosed in U.S. Pat. No. 3,645,992 (Elston), thedisclosure of which is incorporated herein by reference.

In general, the continuous polymerization useful for making the ethylenepolymers used in the present invention may be accomplished at conditionswell known in the prior art for Ziegler-Natta or Kaminsky-Sinn typepolymerization reactions, that is, temperatures from 0 to 250° C. andpressures from atmospheric to 1000 atmospheres (100 MPa).

The compositions disclosed herein can be formed by any convenientmethod, including dry blending the individual components andsubsequently melt mixing or by pre-melt mixing in a separate extruder(e.g., a Banbury mixer, a Haake mixer, a Brabender internal mixer, or atwin (or single) screw extruder, including pelletization extrusion).Preferably, the inventive composition is formed by melt mixing in atwin-screw co-rotating extruder.

Another suitable technique for making the composition is in-situpolymerization such as provided in pending U.S. Ser. No. 08/010,958,entitled “Ethylene Interpolymerizations”, which was filed Jan. 29, 1993in the names of Brian W. S. Kolthammer and Robert S. Cardwell, thedisclosure of which is incorporated herein in its entirety by reference.U.S. Ser. No. 08/010,958 describes, inter alia, interpolymerizations ofethylene and C₃-C₂₀ alpha-olefins using a homogeneous catalyst in atleast one reactor and a heterogeneous catalyst in at least one otherreactor and this method can be adapted to employ a polypropylenepolymerization reactor as a substitute for the heterogeneous catalyzedethylene polymerization reactor or as an additional reactor. That is,the in situ polymerization can comprise at least three reactors where atleast two reactors provide the ethylene polymer (as a polymer blendcomposition) and at least one reactor provide the reactor gradepolypropylene polymer. For in situ polymerizations, the multiplereactors can be operated sequentially or in parallel. But preferably,when in situ polymerization is used it is only employed to providesuitable ethylene polymers (or ethylene polymer blend compositions) andnot the inventive composition itself.

Preferably, the fiber of the invention will be a multiconstituent ormulticomponent fiber. The inventive multiconstituent fiber can be staplefibers, spunbond fibers, melt blown fibers (using, e.g., systems asdisclosed in U.S. Pat. No. 4,340,563 (Appel et al.), U.S. Pat. No.4,663,220 (Wisneski et al.), U.S. Pat. No. 4,668,566 (Braun), U.S. Pat.No. 4,322,027 (Reba), U.S. Pat. No. 3,860,369, all of which areincorporated herein by reference), gel spun fibers (e.g., the systemdisclosed in U.S. Pat. No. 4,413,110 (Kavesh et al.), incorporatedherein by reference), and flash spun fibers (e.g., the system disclosedin U.S. Pat. No. 3,860,369, the disclosure of which is incorporatedherein by reference).

As defined in The Dictionary of Fiber & Textile Technology, by HoechstCelanese Corporation, gel spinning refers to “[a] spinning process inwhich the primary mechanism of solidification is the gelling of thepolymer solution by cooling to form a gel filament consisting ofprecipitated polymer and solvent. Solvent removal is accomplishedfollowing solidification by washing in a liquid bath. The resultantfibers can be drawn to give a product with high tensile strength andmodulus.”

As defined in The Nonwoven Fabrics Handbook, by John R. Starr, Inc.,produced by INDA, Association of the Nonwoven Fabrics Industry, flashspinning refers to “a modified spunbonding method in which a polymersolution is extruded and rapid solvent evaporation occurs so that theindividual filaments are disrupted into a highly fibrillar form and arecollected on a screen to form a web.”

Staple fibers can be melt spun (i.e., they can be extruded into thefinal fiber diameter directly without additional drawing), or they canbe melt spun into a higher diameter and subsequently hot or cold drawnto the desired diameter using conventional fiber drawing techniques. Thenovel fibers disclosed herein can also be used as bonding fibers,especially where the novel fibers have a lower melting point than thesurrounding matrix fibers. In a bonding fiber application, the bondingfiber is typically blended with other matrix fibers and the entirestructure is subjected to heat, where the bonding fiber melts and bondsthe surrounding matrix fiber. Typical matrix fibers which benefit fromuse of the novel fibers includes, but is not limited to: poly(ethyleneterephthalate) fibers; cotton fibers; nylon fibers; other polypropylenefibers; other heterogeneously branched polyethylene fibers; and linearpolyethylene homopolymer fibers. The diameter of the matrix fiber canvary depending upon the end use application.

The inventive multiconstituent fibers can also be used to provide asheath/core bicomponent fiber (i.e., one in which the sheathconcentrically surrounds the core). The inventive polymer blend can bein either the sheath or the core. Different inventive polymer blends canalso be used independently as the sheath and the core in the same fiberand especially where the sheath component has a lower melting point thanthe core component. Other types of bicomponent fibers are within thescope of the invention as well, and include such structures asside-by-side fibers (e.g., fibers having separate regions of polymers,wherein the inventive polymer blend comprises at least a portion of thefiber's surface): One embodiment is in a bicomponent fiber wherein thepolymer blend composition disclosed herein is provided in the sheath,and a higher melting polymer, such as polyester terephthalate or adifferent polypropylene is provided in the core.

The shape of the fiber is not limited. For example, typical fiber have acircular cross sectional shape, but sometimes fibers have differentshapes, such as a trilobal shape, or a flat (i.e., “ribbon” like) shape.The fiber disclosed herein is not limited by the shape of the fiber.

Fiber diameter can be measured and reported in a variety of fashions.Generally, fiber diameter is measured in denier per filament. Denier isa textile term which is defined as the grams of the fiber per 9000meters of that fiber's length. Monofilament generally refers to anextruded strand having a denier per filament greater than 15, usuallygreater than 30. Fine denier fiber generally refers to fiber having adenier of 15 or less. Microdenier (also referred to as “microfiber”)generally refers to fiber having a diameter not greater than 100micrometers. For the novel fibers disclosed herein, the diameter can bewidely varied. But the fiber denier can be adjusted to suit thecapabilities of the finished article and as such, would preferably befrom 0.5 to 30 denier/filament for melt blown; from 1 to 30denier/filament for spunbond; and from 1 to 20,000 denier/filament forcontinuous wound filament.

Fabrics made from the inventive fibers include both woven and nonwovenfabrics. Nonwoven fabrics can be made variously, including spunlaced (orhydrodynamically entangled) fabrics as disclosed in U.S. Pat. No.3,485,706 (Evans) and U.S. Pat. No. 4,939,016 (Radwanski et al.), thedisclosures of which are incorporated herein by reference; by cardingand thermally bonding staple fibers; by spunbonding continuous fibers inone continuous operation; or by melt blowing fibers into fabric andsubsequently calendering or thermally bonding the resultant web. Thesevarious nonwoven fabric manufacturing techniques are well known to thoseskilled in the art and the disclosure is not limited to any particularmethod. Other structures made from such fibers are also included withinthe scope of the invention, including e.g., blends of these novel fiberswith other fibers (e.g., poly(ethylene terephthalate) (PET) or cofton).

Optional additive materials for use in the present invention includepigments, antioxidants, stabilizers, surfactants (e.g., as disclosed inU.S. Pat. No. 4,486,552 (Niemann), U.S. Pat. No. 4,578,414 (Sawyer etal.) or U.S. Pat. No. 4,835,194 (Bright et al.), the disclosures of allof which are incorporated herein by reference).

In preferred embodiments of the invention, at bonding temperatures lowerthan the peak elongation temperature (where peak elongation temperatureis the temperature of the maximum elongation), fabrics prepared fromfibers of the invention will exhibit a fabric elongation which is atleast 20 percent, more preferably at least 50 percent, and mostpreferably at least 100 percent greater than that of fabric preparedwith fibers prepared from the unmodified polypropylene used as thesecond polymer.

In preferred embodiments of the invention, at bonding temperatures atleast 10° C. less than the peak strength bonding temperature (i.e., thebonding temperature of the maximum strength (tenacity)), fabricsprepared from fibers of the invention will exhibit a fabric strengthwhich is at least 25 percent, more preferably at least 50 percent, andmost preferably at least 70 percent higher than the a fabric preparedfrom fiber prepared from the unmodified polypropylene polymer used asthe second polymer. The improvement is particularly important becauseattaining a given tenacity at a comparatively lower thermal bondinginvariably promotes the highly desirably performance property ofenhanced fabric softness.

In preferred embodiments of the invention, fibers of the invention willexhibit a spinnability (maximum draw rpms) which is no more than 25percent less than, more preferably no more than 15 percent less than thespinnability (maximum draw rpms) of fiber prepared from the unmodifiedpolypropylene polymer used as the second polymer. Draw rpms may also becorrelated to draw pressure on a spunbond process.

Useful articles which can be made from the polymer compositionsdisclosed herein include films, fibers, thermoformed articles, moldedarticles (for example, blow molded articles, injection molded articlesand rotomolded articles) and coated articles (for example, extrusioncoatings). Other useful articles included woven and nonwoven items suchas those described in issued U.S. Pat. No. 5,472,775 (Obijeski et al.),incorporated herein by reference.

The subject invention is particularly usefully employed in thepreparation of calendar roll bonded fabrics such as carded staple fabricor spunbonded fabrics. Exemplary enduse articles include, but notlimited to, diaper and other personal hygiene article components,disposable clothing (such as hospital garments), durable clothing (suchas insulated outerwear), disposable wipes, dishcloths, and filter media.

The subject invention is also usefully employed in the bonding of carpetor upholstery components, and in the bonding and/or strengthening ofother webs (such as industrial shipping sacks, strapping and rope,lumber wraps, house/construction wraps, pool covers, geotextiles, andtarpaulins).

The subject invention may further find utility in adhesive formulations,optionally in combination with one or more tackifiers, plasticizers, orwaxes.

EXAMPLES

In an evaluation to determine the effect of ethylene polymers on thefiber spinning, bonding and elongation properties of polypropylenepolymers, a minor amount of various ethylene polymers were separatelyadmixed with a Ziegler-catalyzed isotactic polypropylene polymer,INSPIRE™ H500-35, supplied by The Dow Chemical Company. Thepolypropylene polymer was supplied with a visbroken melt flow rate of 35g/10 minutes at 230° C./2.16 kg. The various ethylene polymers used inthe evaluation are listed in Table 1.

In this evaluation, polypropylene/ethylene polymer blends were preparedby tumble dry-blending followed by melt extrusion and pelletization. Tothe dry-blends, 1000 ppm Irgafos 168 was added via a 5 weight percentmaster batch concentrate comprising INSPIRE™ H500-35 as the carrierresin. The melt extrusion and pelletization were performed using aco-rotating twin-screw Werner Pflieder ZSK-30 (30 mm) extruder at a melttemperature of about 190° C. The extruder was equipped with positiveconveyance elements and no negative conveyance elements. The resultantpolymer blends and the control INSPIRE™ H500-35 polypropylene polymer(comparative example 4) were all meltspun into fiber. Table 2 providesthe weight percentage information for the various examples.

TABLE 1 Product I₂, Melt Type/ Index, g/10 Density, Resin Designationmin. g/cm³ EP1 ENGAGE 8150* 0.5 0.87 EP2 ENGAGE 8100* 1 0.87 EP3 ENGAGE8200* 5 0.87 EP4 AFFINITY PL 1280* 6 0.90 EP5 ESI 5 <15 wt. %‡ EP6ENGAGE 8400* 30 0.87 EP7 SLEP 30 0.913 EP8 ASPUN 6811A 27 0.941 ‡Ratherthan density, the reported value is percent crystallinity as determinedusing differential scanning calorimetry (DSC). Except for the ENGAGEelastomers, all of the above ethylene polymers are available from TheDow Chemical Company. ESI denotes a substantially randomethylene/styrene interpolymer which contains about 30 weight percentstyrene interpolymerized with ethylene. SLEP denotes a homogeneouslybranched substantially linear ethylene/1-octene interpolymermanufactured using a constrained geometry catalyst system in acontinuous polymerization reaction system. ENGAGE is a trademark ofDupont-Dow Elastomers for ethylene elastomers. AFFINITY is a trademarkof The Dow Chemical Company for ethylene plastomers. Both AFFINITY andENGAGE resins are manufactured in a continuous polymerization reactionsystem. ASPUN is a trademark of The Dow Chemical Company for fiber-gradelinear low density polyethylene (LLDPE) resins manufactured using aZiegler titanium catalysis system.

TABLE 2 Ethylene Weight Percent Ethylene Example Polymer Polymer Inv. Ex1 EP1 5 Inv. Ex 2 EP1 1 Inv. Ex 3 EP1 20 Inv. Ex 5 EP2 2 Inv. Ex 6 EP210 Comp. Ex 7 EP3 5 Inv. Ex 8 EP4 5 Inv. Ex 9 EP5 5 Comp. Ex 10 EP6 5Comp. Ex 11 EP7 5 Comp. Ex 12 EP8 5 Comp. Ex 13 EP3 1 Comp. Ex 14 EP6 1Comp. Ex 15 EP6 10

Fiber spinning was conducted on an Alex James laboratory scale spinningapparatus (available from Alex James, Inc.). The various examplecompositions were fed separately into a 1 inch×24 inches single screwextruder, with melt temperature varying from 195° C. to 220° C. Themolten example compositions were forwarded to a Zenith gear pump at1.752 cc/rev. and through a triple screen configuration (20/400/20mesh). The molten example compositions then exited through a spinneretcontaining 108 holes, each with a diameter of 400 μm, wherein the^(L)/_(D) of the holes was 4/1. The molten example compositions weredrawn-down at 0.37 grams/minute from each hole and air cooled by aquench chamber.

The drawn-down fibers were moved down 3 meters to a 6 inch diameter feedgodet, then a 6 inch diameter winder godet. The godets were set to2000-2200 rotations per minute (rpm), imparted no cold drawing anddelivered fibers having diameters in the range of from about 3.0 toabout 3.5 denier. Fiber samples were collected for 2 minutes on thesecond godet for each example composition and then cut from the godet.Each example was then cut into 1 inch to 1.5 inch lengths known asstaple fibers and allowed to relax for minimum 24 hours to promotelaboratory consistency.

All of the example compositions spun well, providing fine denier staplefibers. However, the good spinning performance of the Inventive Examples(all comprising an ethylene polymer having an I₂ melt index less than orequal to 5 g/10 minutes) was surprising because the various ethylenepolymers used as the blend component for the inventive compositions donot spin on the above-described spinning apparatus when used alone. Thatis, as taught by Jezic et al. in U.S. Pat. No. 4,839,228, for successfulfiber-spinning, ethylene polymers having an I₂ melt index greater thanor equal to about 12 g/10 minutes are typically used and not the kind ofhigh molecular weight ethylene polymers required in the presentinvention.

The staple fibers of each example composition were weighed out as 1.25 gspecimens, typically 4-8 specimens per sample. The 1.25 g specimens werefed to a SpinLab Rotor Ring 580 set at maximum speed for 45 seconds tocard the fibers and provide an initial web. After the first carding, thefibers were removed, re-fed to the SpinLab Rotor Ring 580 unit, andre-carded for another 45 seconds. After the second carding, a 3.5 inchfiber web for each example was removed and placed in a 3.5 inch by 12inch metal feed tray.

A photomicrograph of the cross-section of carded staple fibers ofInventive Example 1 was taken (FIG. 1). Prior to taking thephotomicrograph, the carded staple fibers were stained withRuCI₃/hypochlorite and mounted with Epofix™. The photomicrograph itselfshows, prior to thermal bonding, the cross-sectional configuration ofthe polypropylene polymer (continuous polymer phase) and the ethylenepolymer (the discontinuous phase) is of the island-sea type with thepolypropylene polymer constituting more than 50 percent of the surfaceof the carded staple fiber. That is, the discontinuous phase did notoccupy a substantial portion of the fiber surface prior to thermalbonding. The same result and characteristic is shown in FIGS. 2 and 3for Inventive Examples 3 and 9, respectively. In addition to indicatingthe discontinuous phase is distinct, not highly dispersed (relativelylarger particles) and occupies about as much of the surface of the fiberas the weight percent amount contained therein (i.e., there is nopreferential migration or substantially higher concentration at thesurface), FIG. 3 also shows that the discontinuous substantially randomESI phase has at least two components. This multi-componentdiscontinuous phase is shown as substantially circular particles withdark stained peripheries which may relate to the amount of atacticpolymer present in the interpolymer. In contrast to FIGS. 1-3, FIG. 4and FIG. 5 indicate that comparative examples are characterized by asubstantially higher degree of dispersion (smaller discontinuous phaseparticles) and miscibility between the phases (less discontinuous phasedistinctiveness). FIGS. 1-5 were all taken at 15,000× magnification.

The carded staple fibers of each example composition were bonded using atwo-roll thermal bonding unit (that is, a Beloit Wheeler Model 700Laboratory Calendar). The top roll had a 5 inch diameter and a 12 inchface and consisted of hardened chromed steel embossed in a squarepattern at 20 percent coverage. The bottom roll was the same, except notembossed. For thermal bonding, the bond rolls were set at 1000 psi,which was equivalent to 340 pounds per linear inch (pli) for this unit.The conversion calculation was as follows: 1000 psi−400 psi for lowerroll to overcome spring force=600 psi×1.988 square inch cylinderareal3.5 inches web width=340 pli.

The temperatures of the bond rolls were set to maintain about a 3° C.differential, with the top roll always being cooler to minimizesticking. The bond rolls were also set to range in temperature fromabout 118° C. to about 137° C. (top roll temperature) and 115° C. to134° C. (bottom roll temperature). The rolls were rotated at 23.6feet/minutes. The fiber webs were then passed between the two rolls andremoved from the side opposite the feed area. The resultant nonwovenembossed fabrics which had a nominal weight basis of 1 ounce per squareyard were then cut into 1 inch×4 inches fabric specimens.

Before performance testing, each fabric specimen was weighed and theweight entered into a computer program. The 1 inch×4 inches specimenswere positioned lengthwise on a Sintech 10D tensiometer equipped with a200 pound load cell, such that 1 inch at each end of the specimen wasclamped in the top and bottom grips. The specimens were then pulled, oneat a time, at 5 inches/minutes to their breaking point. The computerthen used the dimensions of the specimen and the force exerted tocalculate the percent strain (elongation) experienced by the specimenand the normalized force at break (tensile break which was taken as thebond strength for the example) in grams. Four measurements were taken ateach bonding temperature for each example. Table 3 provides the thermalbonding bond strength performance results for the various carded staplefabric examples. Table 4 provides the thermal bonding elongationperformance results for the various carded staple fabric examples. FIGS.6-15 provide various comparisons between Inventive Examples 1, 2, 3, 5,6, 8 and 9 and comparative examples 4, 5, 7, 10, 11, 12, 13, 14 and 15.

TABLE 3 Bond Strength, grams Top Roll, embossed, Temp., ° C. 118 120 123127 130 133 137 Inv. Ex 1 ND ND 2769 3272 3251 4075 4457 Inv. Ex 2 18421928 2150 2756 2704 3578 3975 Inv. Ex 3 3509 4039 4337 4551 4289 41334329 Comp. Ex 4 1843 2028 1831 2332 2464 3278 3431 Inv. Ex 5 2051 21003387 2784 2909 4080 4491 Inv. Ex 6 3240 3367 3558 3936 4110 4897 4574Comp. Ex 7 1781 1809 2171 2545 2403 2965 3610 Inv. Ex 8 1992 2129 20092626 2672 3454 4389 Inv. Ex 9 3029 3307 3344 3886 4468 4497 3646 Comp.Ex 10 1780 1774 1819 2092 2764 3542 3560 Comp. Ex 11 1651 1625 1695 20432507 3125 3970 Comp. Ex 12 1692 1738 1961 2161 2488 3301 3772 Comp. Ex13 2095 2054 2037 2275 2251 3295 4311 Comp. Ex 14 1528 1630 2146 19652083 3047 3659 Comp. Ex 15 1914 2198 2111 2493 2882 3167 3745

Table 3 and FIGS. 6-10 show all Inventive Examples, at a top embossedroll temperature of 127-130° C., are generally characterized as havingbond strengths greater than or equal 2,500 grams and Inventive Examples1, 3, 6 and 9 are preferentially characterized as having dramaticallyimproved bond strengths at greater than or equal to 3,250 gram. That is,bond strengths of Inventive Examples 1, 3, 6 and 9 were greater than 36percent higher (and up to 84 percent) higher than the bond strength ofthe polypropylene polymer at a top embossed roll temperature of 127-130°C.

Table 3 and FIGS. 6-10 also show where the I₂ melt index of the ethylenepolymer is relatively high (that is, greater than or equal to 5 g/10minutes) and the ethylene polymer is an ethylene/□-olefin interpolymer(for example, where the α-olefin is 1-hexene, 1-butene or 1-octene), theinventive composition will be characterized as comprising an ethylenepolymer which has a polymer density greater than 0.87 g/cm³, preferablygreater than or equal 0.90 g/cm³, and more preferably greater than orequal to 0.94 g/cm³.

TABLE 4 Percent Elongation Top Roll, embossed, Temp., ° C. 118 120 123127 130 133 137 Inv. Ex 1 ND ND 20 23 27 36 37 Inv. Ex 2 11 12 12 17 1824 28 Inv. Ex 3 42 56 53 60 55 50 54 Comp. Ex 4 11 11 12 14 14 19 23Inv. Ex 5 13 12 18 21 20 33 39 Inv. Ex 6 24 27 27 30 35 44 41 Comp. Ex 711 12 13 14 17 22 25 Inv. Ex 8 15 15 13 19 19 25 36 Inv. Ex 9 55 66 106127 107 105 60 Inv. Ex 10 69 73 69 83 90 75 45 Comp. Ex 11 13 14 14 1620 27 30 Comp. Ex 12 11 11 11 13 16 22 32 Comp. Ex 13 11 11 12 14 16 2532 Comp. Ex 14 15 14 14 15 18 24 36 Comp. Ex 15  9 10 11 11 12 19 24Comp. Ex 16 16 16 18 19 21 26 30

Further, Table 3 and FIGS. 6-10 also show that in addition toethylene/α-olefin interpolymers (Inventive Examples 1, 3 and 6), otherhigh molecular weight thylene polymers such as high molecular weightethylene/styrene interpolymers (Inventive Example 9) can dramaticallyimprove the fiber bond strength of isotactic polypropylene polymers.This data also suggests that the same result can be obtained with highmolecular weight ethylene homopolymers (HMW-HDPE).

FIGS. 11-15 and Table 4 show that in addition to improved bond strength,the inventive composition also provides improved fiber elongation; thatis, at a thermal bonding temperature of 127-130° C., all inventivecompositions had elongations greater than 15 percent and preferredinventive compositions (Inventive Examples 3, 6 and 9) had elongationsgreater than or equal to 30 percent at a thermal bonding temperature of127-130° C. This result is surprising and unexpected because bondstrength improvements tend to reduce elongation performance (and viceversa). For example, comparative example 10 had a lower bond strength at127° C. than the polypropylene polymer while this comparative examplealso had a higher percent elongation than the polypropylene polymer at127° C.

In another evaluation, the effect of blending a minor amount of a highmolecular weight ethylene polymer in a Ziegler-catalyzed polypropylenepolymer and a metallocene-catatyzed polypropylene polymer wasinvestigated. The Ziegler-catalyzed polypropylene polymer and the highmolecular weight ethylene polymer (EP2) were the same as used inInventive Example 5 above. The reactor grade metallocene-catalyzedpolypropylene polymer in the evaluation had a MFR of 22 g/10 minutesmelt flow rate (ASTM D-1238, Condition 230° C./2.16 kg) and was soldunder the designation of ACHIEVE 3904 by Exxon Chemicaf Corporation.

This evaluation consisted of four different polymer compositions; eachpolypropylene polymer was evaluated as a control resin and for the othertwo examples, each polypropylene polymer was melt blended/extruded with1000 ppm Irgafos 168 and 5 weight percent of ENGAGE Elastomer 8100 (anethylene/1-octene interpolymer supplied by Dupont-Dow Elastomers) usingthe above-described master batch concentrate and ZSK-30 extruder atabout 190° C. Each control propylene polymer was also meltblended/extruded with 1000 ppm Irgafos 168 using the above-describedmaster batch concentrate and the ZSK-30 extender at about 190° C. Thepolypropylene polymer/ethylene polymer blend that comprised theZiegler-catalyzed polypropylene polymer was designated Inventive Example16. The polypropylene polymer/ethylene polymer blend that comprised themetallocene-catalyzed polypropylene polymer was designated InventiveExample 17. The Ziegler-catalyzed polypropylene polymer was designatedcomparative example 18 and the ACHIEVE 3904 metallocene-catalyzedpolypropylene polymer was designated comparative example 19. Eachpolymer composition was spun into fine denier staple fibers as describedabove for Inventive Example 1 and was also carded as described above.The carded staple fibers for were tested for bond performance using thesame methods and procedure described above for Inventive Example 1. FIG.16 graphically shows the thermal bonding performance results for thefour example compositions. The results in FIG. 12 indicate that a highweight ethylene polymer at nominal amounts can dramatically improve thethermal bonding performance of both isotactic andmetallocene-polypropylene polymers and that improvements are especiallysubstantial and surprising stable across a broad bond temperature rangewith the metallocene-polypropylene polymer.

FIGS. 17-20 are photomicrograph of thermally bonded fibers. FIG. 17shows that very little shrink or stress is associated with the inventivefiber (FIG. 17(b)) relative to the comparative fiber (FIG. 17(d)). FIG.18 shows that substantially more melting and flowing is associated withthe inventive fiber (FIGS. 18(a) and (b)) relative to the comparativefiber (FIGS. 18(c) and (d)). FIG. 19 shows at least four differentinventive fibers at different viewing perspectives at a thermal bondedsite magnified 15,000×. The different perspectives show, for theinventive fiber (Inventive Example 1), the discontinuous ethylenepolymer phase (dark stained areas) does not occupy a substantial portionof a respective fiber surface after thermal bonding. At 15,000×magnification, FIG. 20 shows there is some crazing associated withpolypropylene polymers.

In another evaluation to investigate thermal bonding performance, aminor amount of various high molecular weight ethylene polymers wereseparately blended with a visbroken Ziegler-catalyzed polypropylenepolymer and compared to the neat visbroken Ziegler-catalyzedpolypropylene polymer, a neat reactor grade metallocene-catalyzedpolypropylene polymer and a neat reactor grade Ziegler-catalyzedpolypropylene polymer. The visbroken Ziegler-catalyzed polypropylenepolymer (comparative example 18) was the same as used in InventiveExample 1 above. The reactor grade metallocene-catalyzed polypropylenepolymer (comparative example 19) was the same above; that is, it had aMFR of 22 g/10 minutes melt flow rate (ASTM D-1238, Condition 230°C./2.16 kg) and was sold under the designation of ACHIEVE 3904 by ExxonChemical Corporation. The reactor grade Ziegler-catalyzed polypropylenepolymer (comparative example 20) had a MFR of 25 g/10 minutes melt flowrate (ASTM D-1238, Condition 230° C./2.16 kg).

The various high molecular weight ethylene polymers used in thisevaluation are listed in Table 5 below.

TABLE 5 I₂, Melt Product Index, g/10 Density, Resin Type/Designationmin. g/cm³ EP9 HDPE 05862 5 0.962 EP10 SLEP 0.7 0.960 EP11 ESI DE 1000.5 30 wt. %^(‡) EP12 ESI DS 100 0.5 70 wt. %^(‡) EP13 ENGAGE* 8180 0.50.863 ^(‡)Rather than density, the reported value is weight percentstyrene. Except for ENGAGE 8180, all of the above ethylene polymers areavailable from The Dow Chemical Company. ESI denotes a substantiallyrandom ethylene/styrene interpolymer. SLEP denotes a homogeneouslybranched substantially linear ethylene/1-octene interpolymermanufactured using a constrained geometry catalyst system in acontinuous polymerization reaction system. ENGAGE is a trademark ofDupont-Dow Elastomers for ethylene elastomers. ENGAGE elastomers aremanufactured in a continuous polymerization reaction system using aconstrained geometry catalyst system. HDPE 05862 manufactured using aZiegler catalysis system.

Table 6 below provides the polymer weight percentage information for theexamples investigated in this evaluation.

TABLE 6 Ethylene Weight Percent Ethylene Example Polymer Polymer Comp.Ex 21 EP9  5 Inv. Ex 22 EP10 5 Comp. Ex 23 EP11 5 Inv. Ex 24 EP12 5 Inv.Ex 25 EP10/EP13 2.5/2.5 Comp. Ex 26 EP9  8

Each of the ethylene polymer/polypropylene polymer combinations weremelt blended/extruded with 1000 ppm Irgafos 168 on a ZSK-30 twin-screwco-rotating extruder at about 190° C. Comparative example 18, a controlpropylene polymer, was also melt blended/extruded with 1000 ppm Irgafos168 the ZSK-30 extruder at about 190° C.

Each polymer composition was spun into fine denier staple fibers asdescribed above for Inventive Example 1 and was also carded as describedabove. The carded staple fibers for were tested for bond performanceusing the same methods and procedures described above for InventiveExample 1. Table 7 provides the thermal bonding bond strength (tenacity)performance results at 1 oz/yd²for the various carded staple fabricexamples. Table 8 provides the thermal bonding elongation performanceresults at 1 oz/yd² for the various carded staple fabric examples.

TABLE 7 Bond Strength, grams Top Roll, embossed, Temp., ° C. 120 123 127130 133 137 140 Comp. Ex 18 1608 1553 1836 1813 2112 3165 3725 Comp. Ex19 ND 2080 1825 2288 2361 3263 3573 Comp. Ex 20 ND 1816 1776 2024 20432559 2839 Comp. Ex 21 1608 1643 2025 2001 2532 3113 3980 Inv. Ex 22 25452709 3157 3872 4693 4872 4644 Comp. Ex 23 1965 2237 2249 2479 2899 34524231 Inv. Ex 24 2117 2521 2829 3100 3637 3836 5048 Inv. Ex 25 2288 27923383 3851 4092 4780 4329 Comp. Ex 26 ND 1817 2217 2492 2709 3312 4640

TABLE 8 Percent Elongation Top Roll, embossed, Temp., ° C. 120 123 127130 133 137 140 Comp. Ex 18  8 8 9 11 13 15 27 Comp. Ex 19 ND 10 8 11 1219 24 Comp. Ex 20 ND 8 9 10 10 13 15 Comp. Ex 21  9 9 11 14 17 23 37Inv. Ex 22 24 26 34 53 85 80 59 Comp. Ex 23 12 14 13 18 22 27 38 Inv. Ex24 15 18 19 23 30 35 54 Inv. Ex 25 24 30 40 55 70 80 52 Comp. Ex 26 ND10 12 15 18 23 40

Table 7 shows all Inventive Examples, at a top embossed roll temperatureof 127-130° C., are generally characterized as having bond strengthsgreater than or equal 2,500 grams. That is, in this bond temperaturerange, the bond strengths of Inventive Examples 22, 24 and 25 were about26 to about 114 percent higher (than the bond strengths of the neatpolypropylene polymer compositions (comparative examples 18, 19 and 20)and the composition comprising 5 g/10 minutes I₂Ziegler-catalyzed HDPE(comparative example 21). Table 7 also shows that for ethylene/styreneinterpolymers comprising 30 weight percent styrene or less, the I₂ meltindex must be in the range of greater than 0.5 g/10 minutes to less thanor equal to 10 g/10 minutes to ensure substantially improved tenacity.

Table 8 shows the inventive composition provides even more dramaticimprovements in respect of elongation. Specifically, at a top embossedroll temperature of 127-130° C., the percent elongations of InventiveExamples 22, 24 and 25 were about 28 percent up to 450 percent higherthan the percent elongations of comparative examples 18, 19, 20 and 21.

We claim:
 1. A method for improving the bonding strength of a fibercomprising: obtaining a mixture of at least one polypropylene resin withless than or equal to 22 weight percent of at least one ethylene polymerhaving a density of from about 0.85 to about 0.97 g/cm³ and an I₂ meltindex of from about 0.01 to about 10 grams/10 minutes, wherein the fiberis characterized as being thermally bondable at 340 pounds/linear inch(pli) and a bond roll surface temperature in the range of 127 to 137°C.; and forming a fiber from the mixture.
 2. The method of claim 1,wherein the ethylene polymer is an ethylene homopolymer or anethylene/α-olefin interpolymer.
 3. The method of claim 2, wherein theethylene/α-olefin interpolymer comprises ethylene and at least oneC₃-C₂₀ α-olefin.
 4. The method of claim 1, wherein the ethylene polymeris a substantially linear ethylene/α-olefin interpolymer characterizedas having: (A) a melt flow ratio (I₁₀/I₂)>5.63, (B) a molecular weightdistribution, M_(w)/M_(n), defined by the inequality:M_(w)/M_(n)<(I₁₀/I₂)−4.63, and (C) a critical shear rate at the onset ofsurface melt fracture which is at least 50 percent greater than thecritical shear rate at the onset of surface melt fracture of a linearethylene/α-olefin interpolymer having the about same I₂ and M_(w)/M_(n).5. The method of claim 1, wherein the polypropylene resin is a reactorgrade polypropylene and has a MFR at 230° C./2.16 kg greater than orequal 20 g/10 minutes.
 6. The method of claim 1, wherein thepolypropylene resin is a visbroken polypropylene and has a melt flowrate at 230° C./2.16 kg of greater than or equal 20 g/10 minutes.
 7. Themethod of claim 1, wherein the polypropylene resin has a coupled meltflow rate at 230° C./2.16 kg of greater than or equal 20 g/10 minutes.8. The method of claim 1, wherein the polypropylene resin ismanufactured using a single-site, metallocene or constrained geometrycatalyst system.
 9. The method of claim 1, wherein the polypropyleneresin is characterized as having at least 96 percent weightisotacticity.
 10. The method of claim 1, wherein the ethylene polymerhas an I₂ melt index less than 5 g/10 minutes, when the density of theethylene polymer is greater than 0.94 g/cm³.
 11. The method of claim 1,wherein the fiber comprises a continuous polymer phase and at least onediscontinuous polymer phase.
 12. The method of claim 11, wherein the atleast one discontinuous polymer phase comprises from about 0.1 percentto about 30 weight percent (by weight of the fiber) an at least oneethylene polymer having: i. an I₂ melt index less than or equal to 10grams/10 minutes, and iii. a density of from about 0.85 to about 0.97grams/centimeters³, and wherein the continuous polymer phase comprises apolypropylene polymer having melt flow rate (NFR) at 230° C./2.16 kggrater than or equal to 12 grams/10 minutes.
 13. The method of claim 4,wherein prior to any bonding operation, the continuous polymer phaseconstitutes more than 50 percent of the fiber surface area and the atleast two polymer phases cross-sectionally provide an island-seaconfiguration.
 14. The method of claim 1, wherein the ethylene polymeris a homogeneously branched ethylene polymer having a compositiondistribution branch index (CDBI) greater than 50 percent.
 15. The methodof claim 14, wherein the homogeneously branched ethylene polymer haslong chain branching.
 16. The method of claim 14, wherein thehomogeneously branched ethylene polymer is a homogeneously branchedlinear ethylene polymer.
 17. The method of claim 14, wherein thehomogeneously branched ethylene polymer is a homogeneously branchedsubstantially linear ethylene polymer.
 18. The method of claim 1,wherein the ethylene polymer is an ethylene/aromatic vinyl or vinylideneinterpolymer.
 19. The method of claim 18, wherein the interpolymer is anethylene/styrene interpolymer.
 20. The method of claim 1, wherein theethylene polymer is a substantially random ethylene/aromatic vinyl orvinylidene interpolymer.
 21. The method of claim 18, wherein theinterpolymer is a substantially random ethylene/styrene interpolymer.22. The method of claim 19 or 21, wherein the ethylene polymer is asubstantially random ethylene/aromatic vinyl or vinylidene interpolymer.23. The method of claim 19 or 21, wherein the interpolymer containsgreater than or equal to 25 weight percent (based on the total weight ofthe interpolymer) interpolymerized or copolymerized styrene.
 24. Themethod of claim 1, wherein the interpolymer contains greater than orequal 50 weight percent (based on the total weight of the interpolymer)interpolymerized or copolymerized styrene.
 25. The method of claim 1,wherein the fiber further comprises at least one other olefin polymer.26. The method of claim 25, wherein the at least one other olefinpolymer is a high density ethylene polymer having a density greater thanor equal to 0.94 g/Cm³.
 27. The method of claim 26 wherein the highdensity ethylene polymer is a homopolymer polyethylene.